Short answer
No, and Muslims should not argue that it is. Sikhs hold that their faith is its own revelation, not a mixture of two others. A hymn by Guru Arjan, written on a theme of Kabir, says he is neither a Hindu nor a Musalman. The same hymn gives up the Ramadan fast, the pilgrimage to Mecca and the Muslim prayer. It gives up Hindu worship and pilgrimage too, so it cannot be read as half-Islam. Islam does not judge any book, the Qur'an included, by guessing where its words came from. It asks whether the book is from God (﷾), and the Qur'an invites you to test it.
Full explanation
Guru Arjan's hymn at Ang 1136, in full
Sikhism (Sikhs also say Sikhi) has one scripture, the Guru Granth Sahib, which Sikhs honour as their living Guru. Its pages are called Angs. Guru Arjan, the fifth Guru, compiled its first edition, the Adi Granth. At Ang 1136, in the raga (musical mode) Bhairao, stands a hymn by Guru Arjan, headed Mahala 5 (the fifth Guru). Macauliffe, in his English translation (Oxford, 1909), says it was written on a theme of Kabir, and the hymn closes with Kabir's name. His rendering of the whole hymn is shown below. The speaker keeps no Ramadan fast and goes on no pilgrimage to Mecca (Makka in Macauliffe's spelling). He does not pray as the Musalmans. He also does not worship as the Hindus and does not go to Hindu places of pilgrimage. He says he is neither a Hindu nor a Musalman. In the hymn's words, soul and body belong to God (﷾) whether He is called Allah (﷾) or Ram.
“I practise not fasting, nor observe the Ramzan: I serve Him who will preserve me at the last hour. The one Lord of the earth is my God, Who judgeth both Hindus and Musalmans. I go not on a pilgrimage to Makka, nor worship at Hindu places of pilgrimages. I serve the one God and none other. I neither worship as the Hindus, nor pray as the Musalmans. I take the Formless God into my heart, and there make obeisance unto Him. I am neither a Hindu nor a Musalman. The soul and body belong to God whether He be called Allah or Ram. Kabir hath delivered this lecture. When I meet a true guru or pir, I recognize my own Master.”
Sikhs say their faith is its own
Sikhs do not describe the teaching of Guru Nanak (Sikhs say Guru Nanak Dev Ji) as a mixture of two faiths. They hold that the word came to him from God (﷾). In Ang 722 he says, "As the word of the Lord cometh to me, so I make known". Guru Arjan says in Ang 628 that the bani, the hymn, came from the Primal Lord. The historian J. S. Grewal writes that Guru Nanak claims divine sanction for his message and complete originality for his faith. Grewal adds that one does not have to believe in revelation to see that this is what Guru Nanak claims.
“As the word of the Lord cometh to me, so I make known, O Lalo”
In a Sorath hymn Guru Arjan, the fifth Guru, says that the bani (the hymn, the Word) came from the Primal Lord, and that it removes all anxiety. Sikhs often cite this line for the teaching that Gurbani comes from God.
Grewal, a historian of the Sikhs, reviews the work of W. H. McLeod. He reports that McLeod, in Guru Nanak and the Sikh Religion (1968), held that Guru Nanak thought Hindu and Islamic beliefs fundamentally wrong and that his religion is not a synthesis of Hindu and Islamic beliefs, but also called the pattern he set a reworking of the Sant synthesis. Grewal agrees that Guru Nanak treats the Brahmanical, ascetic and Islamic traditions as none of them authoritative. He answers that McLeod passes over Guru Nanak's own statements of divine sanction: one does not have to believe in revelation to see that Guru Nanak claims complete originality for his faith.
What historians say about the origins
W. H. McLeod, a leading Western historian of the Sikhs, did not call Sikhism a mixture of Hindu and Islamic beliefs. In his 1968 study of Guru Nanak he held that Guru Nanak thought both sets of beliefs fundamentally wrong. McLeod also placed Guru Nanak in the Sant tradition, the poet-saints of north India, with Kabir, Ravidas and Nam Dev among them. Other historians, such as Grewal, stress Guru Nanak's own claim to divine sanction for his message and to complete originality. Historians still argue over this. Islam does not need to settle the argument. Finding similar ideas in earlier teachers does not decide whether a book is from God (﷾).
Grewal, a historian of the Sikhs, reviews the work of W. H. McLeod. He reports that McLeod, in Guru Nanak and the Sikh Religion (1968), held that Guru Nanak thought Hindu and Islamic beliefs fundamentally wrong and that his religion is not a synthesis of Hindu and Islamic beliefs, but also called the pattern he set a reworking of the Sant synthesis. Grewal agrees that Guru Nanak treats the Brahmanical, ascetic and Islamic traditions as none of them authoritative. He answers that McLeod passes over Guru Nanak's own statements of divine sanction: one does not have to believe in revelation to see that Guru Nanak claims complete originality for his faith.
Why Muslims should not call it a blend
There are three reasons. The first is accuracy: the hymn above gives up the rites of both faiths, and Sikhs reject the label. The second is consistency. The Meccans said a man was teaching the Prophet (ﷺ) (16:103), and that his recitation was tales of the ancients written down for him (25:5). The Qur'an answered the first with a fact: the man they named spoke a foreign tongue, while the Qur'an is clear Arabic (16:103). It answered the second by saying it was sent down by Him who knows the mystery of the heavens and the earth (25:6). It also challenges anyone who says it was forged to bring one sura like it (10:38). Islam answers every claim about a book's sources the same way, with facts and a test, not a guess. The page "Did Muhammad (ﷺ) copy the Qur'an from the Bible?" gives the full answer. The third reason is that finding similar ideas in earlier teachers does not decide whether a book is from God (﷾).
“I practise not fasting, nor observe the Ramzan: I serve Him who will preserve me at the last hour. The one Lord of the earth is my God, Who judgeth both Hindus and Musalmans. I go not on a pilgrimage to Makka, nor worship at Hindu places of pilgrimages. I serve the one God and none other. I neither worship as the Hindus, nor pray as the Musalmans. I take the Formless God into my heart, and there make obeisance unto Him. I am neither a Hindu nor a Musalman. The soul and body belong to God whether He be called Allah or Ram. Kabir hath delivered this lecture. When I meet a true guru or pir, I recognize my own Master.”
“We know indeed that they say, "It is a man that teaches him." The tongue of him they wickedly point to is notably foreign, while this is Arabic, pure and clear.”
“And they say: "Tales of the ancients, which he has caused to be written: and they are dictated before him morning and evening."”
“Say: "The (Qur'an) was sent down by Him who knows the mystery (that is) in the heavens and the earth: verily He is Oft-Forgiving, Most Merciful."”
“Or do they say, "He forged it"? say: "Bring then a Sura like unto it, and call (to your aid) anyone you can besides Allah, if it be ye speak the truth!"”
The test that decides
The Qur'an puts itself to a test any reader can apply. It says a book from anyone other than Allah (﷾) would hold much discrepancy. It also challenges those in doubt to produce one sura like it. These are statements the Qur'an makes about itself, and Islam asks every reader to apply them to the Qur'an with care. The page "Did God speak through the Sikh Gurus?" sets out how the question of the Guru Granth Sahib's origin is to be put.
“Do they not consider the Qur'an (with care)? Had it been from other Than Allah, they would surely have found therein Much discrepancy.”
“And if ye are in doubt as to what We have revealed from time to time to Our servant, then produce a Sura like thereunto; and call your witnesses or helpers (If there are any) besides Allah, if your (doubts) are true.”
“Or do they say, "He forged it"? say: "Bring then a Sura like unto it, and call (to your aid) anyone you can besides Allah, if it be ye speak the truth!"”
The last messenger
Islam's answer to a Sikh reader is the answer it gives to anyone. Weigh the Qur'an by its own challenge, and then ask who the last messenger is. The Qur'an names Muhammad (ﷺ) the Seal of the Prophets, and that is the claim to examine.
“Muhammad is not the father of any of your men, but (he is) the Messenger of Allah, and the Seal of the Prophets: and Allah has full knowledge of all things.”
Five replies answered
Guru Granth Sahib, Ang 1136 — Raga Bhairao, Guru Arjan
“I practise not fasting, nor observe the Ramzan: I serve Him who will preserve me at the last hour. The one Lord of the earth is my God, Who judgeth both Hindus and Musalmans. I go not on a pilgrimage to Makka, nor worship at Hindu places of pilgrimages. I serve the one God and none other. I neither worship as the Hindus, nor pray as the Musalmans. I take the Formless God into my heart, and there make obeisance unto Him. I am neither a Hindu nor a Musalman. The soul and body belong to God whether He be called Allah or Ram. Kabir hath delivered this lecture. When I meet a true guru or pir, I recognize my own Master.”
Cited for
The hymn says soul and body belong to God "whether He be called Allah or Ram", and that the speaker is neither Hindu nor Musalman. That means he is both, a blend.
The response
"Neither" refuses both labels. The line about Allah (﷾) or Ram says, in the hymn's own terms, that soul and body belong to one God (﷾), whatever He is called. The rest of the hymn gives up the Ramadan fast, the pilgrimage to Mecca and the Muslim prayer. It gives up Hindu worship and Hindu pilgrimage as well. A person who keeps the rites of neither faith is not describing a mixture of both.
Where it lands — The hymn names God in two tongues and keeps the rites of neither.
Guru Granth Sahib, Ang 1377 — Salok Sheikh Farid, Sheikh Farid
From Ang 1377 to Ang 1384 the Guru Granth Sahib holds the saloks (couplets) of Sheikh Farid, a Muslim Sufi. Saloks of the Gurus are set among them; one by Guru Amar Das, the third Guru, stands at Ang 1378 among Farid's.
Cited for
Kabir and Sheikh Farid, a Muslim Sufi, are in the Guru Granth Sahib, so it is made of Hindu and Muslim voices.
The response
They are in it, and Islam does not deny that. Sikh tradition says Guru Arjan invited hymns and chose among them, and turned some away. The saloks of the Gurus are set among Farid's, with one of Guru Amar Das at Ang 1378. Who is quoted does not show where a message came from. That is the question of whether it is from God (﷾).
Where it lands — A book that gathers hymns it judged true is not shown to be a blend.
W. H. McLeod and Sikh Studies (2010)
Grewal, a historian of the Sikhs, reviews the work of W. H. McLeod. He reports that McLeod, in Guru Nanak and the Sikh Religion (1968), held that Guru Nanak thought Hindu and Islamic beliefs fundamentally wrong and that his religion is not a synthesis of Hindu and Islamic beliefs, but also called the pattern he set a reworking of the Sant synthesis. Grewal agrees that Guru Nanak treats the Brahmanical, ascetic and Islamic traditions as none of them authoritative. He answers that McLeod passes over Guru Nanak's own statements of divine sanction: one does not have to believe in revelation to see that Guru Nanak claims complete originality for his faith.
Cited for
Historians place Guru Nanak in the Sant tradition, so Sikhism grew out of earlier Indian devotion.
The response
Some historians, McLeod among them, place him in that setting. Others, such as Grewal, stress his own claim to divine sanction and originality. McLeod himself held that his religion is not a synthesis of Hindu and Islamic beliefs. Islam does not enter that debate. Finding similar ideas in earlier teachers does not decide whether a book is from God (﷾).
Where it lands — Finding similar ideas in earlier teachers does not decide whether a book is from God (﷾).
Qur'an 16:103 — Surat al-Nahl (The Bee), verse 103
“We know indeed that they say, "It is a man that teaches him." The tongue of him they wickedly point to is notably foreign, while this is Arabic, pure and clear.”
Cited for
Critics also make claims about where the Qur'an's words came from. Why should Muslims not make the same kind of claim about Sikhism?
The response
The Meccans said a man was teaching the Prophet (ﷺ) (16:103) and that it was tales of the ancients (25:5). The Qur'an answered with a fact, that the man they named spoke a foreign tongue while the Qur'an is clear Arabic. It answered with its source (25:6) and with a challenge to bring one sura like it (10:38). It did not answer with a guess. So Muslims should not call Sikhism a blend. A likeness between books is only a guess about sources, and Islam asks for a test.
Where it lands — A likeness between books is a guess about sources; the test decides whether a book is from God (﷾).
Guru Granth Sahib, Ang 722 — Raga Tilang, Guru Nanak
“As the word of the Lord cometh to me, so I make known, O Lalo”
Cited for
Sikhs say the bani came from God, so Islam must accept that Sikhism is a revelation of its own, as the earlier messengers brought.
The response
Islam does not judge the hearts of the Gurus. It tests a claim of revelation by one standard for every book. The Qur'an offers itself to that standard. It says a book from other than Allah (﷾) would hold much discrepancy, and it challenges doubters to produce a sura like it. Islam does teach that every people had a warner (35:24). It also calls Muhammad (ﷺ) the Seal of the Prophets (33:40), and Guru Nanak came after him. That claim is weighed once the Qur'an has been tested. The page "Did God send prophets to India?" takes up the warners.
Where it lands — The question is whether a book is from God (﷾), and the Qur'an gives the test (4:82; 2:23).
Perspectives
Sikh teaching
Sikhs hold that their faith is its own revelation. Guru Arjan's hymn at Ang 1136 says he is neither a Hindu nor a Musalman and gives up the rites of both.
Guru Arjan's hymn at Ang 1136 says he is neither a Hindu nor a Musalman, and it gives up the rites of both faiths. So Sikhism stands apart from both.
Rebuttal
Islam agrees that the hymn does not make Sikhism half-Islam. But standing apart shows only that a faith is distinct. Whether it is from God (﷾) is tested by what a book claims (4:82; 2:23).
Guru Nanak and Guru Arjan say the bani came to them from the Lord (Ang 722; Ang 628). So the faith is its own revelation, not a blend.
Rebuttal
That is a claim, and Islam tests claims by one standard for every book. The Qur'an offers itself to the same test (4:82; 2:23).
The "blend" reading of Sikhism
Some readers say Sikhism joins Hindu and Islamic teaching. They point to names for God from both faiths, and to the hymns of Kabir and Sheikh Farid. Sikhs reject this.
The Guru Granth Sahib calls God Allah, Khuda and Ram. So, the argument goes, it mixes the language of the two faiths.
Rebuttal
Granted: it uses words for God (﷾) from both languages, and Ang 1136 names Allah and Ram. But the same hymn gives up the rites of both faiths. Using words from two languages does not mix two religions.
Hymns of the Bhagat Kabir and the saloks of Sheikh Farid, a Muslim Sufi, stand in the Guru Granth Sahib beside the Gurus' own. So, the argument goes, it gathers Hindu and Muslim voices.
Rebuttal
Granted. But the book gathers hymns that Guru Arjan chose, and Sikh tradition says he turned some away. Whose hymns are gathered does not show where its message came from, which is the question of whether it is from God (﷾).
What historians say
A leading Western historian of the Sikhs, W. H. McLeod, held that Guru Nanak's religion is not a synthesis of Hindu and Islamic beliefs. He placed it in the Sant tradition of north India, and the historian J. S. Grewal answers that Guru Nanak claims divine sanction and originality.
McLeod held that Guru Nanak thought Hindu and Islamic beliefs were wrong at root. So his religion is not a blend of the two.
McLeod also placed Guru Nanak in the Sant tradition and called his teaching a reworking of the Sant synthesis, a view Grewal disputes. Grewal answers that Guru Nanak's own statements claim divine sanction and complete originality.
The Islamic perspective
Muslims should not call Sikhism a blend. The hymn at Ang 1136 gives up the rites of both faiths, and Sikhs reject the label. Islam answers every claim about a book's sources with facts and a test, not a guess. The question that matters is whether a book is from God (﷾), and the Qur'an gives the test.
The hymn at Ang 1136 gives up the rites of Hindus and Muslims alike, so it cannot be read as half-Islam. Muslims should not claim it is.
The Qur'an records that its first hearers said a man was teaching the Prophet (ﷺ) and that it was tales of the ancients (16:103; 25:5). It answers with a fact, a statement of its source and a challenge (16:103; 25:6; 10:38). Islam answers every claim about a book's sources that way, with facts and a test, not a guess.
Finding similar ideas in earlier teachers does not decide whether a book is from God (﷾). The Qur'an says a book from other than Allah (﷾) would hold much discrepancy, and it challenges doubters to produce a sura like it.
The Qur'an calls Muhammad (ﷺ) the Seal of the Prophets, the last of them. A Sikh reader is invited to weigh that claim by the Qur'an's own test.