Short answer
For much of it, even Christian scholars cannot say. A leading Christian study Bible admits that nobody can be sure who wrote Joshua, Judges, Ruth, Samuel, Kings, Esther, Job or Lamentations. Proverbs names other writers beside Solomon. Only 73 of the 150 Psalms carry David's name. Deuteronomy, said to be by Moses, tells of his death. So a Christian cannot say, book by book, which words came from the prophet whose name is on it. Islam does not say every word in these books is lost: the Qur'an confirms what is true in them (5:48). The Qur'an came through one known Prophet (ﷺ), and the men who wrote it down are known by name.
Full explanation
What a Christian study Bible admits
The NIV Study Bible is a Bible with notes by evangelical scholars, who defend the Bible. Yet book by book its introductions say the writer is unknown or uncertain. This covers Joshua, Judges, Ruth, Samuel, Kings, Chronicles, Esther, Job, Ecclesiastes and Lamentations. It says Job himself did not write the book of Job. It says Solomon was not the only author of Proverbs.
This evangelical study Bible's introductions grant that many Old Testament books have no known author. Joshua: "we are unsure who the final author or editor was". Judges: authorship is "actually uncertain". Ruth: its writer is unknown, and the mention of David implies a later date than Samuel. 1-2 Samuel: who wrote them "cannot be known with certainty". 1-2 Kings: "little conclusive evidence" of who wrote them. Chronicles: the tradition that Ezra wrote it "cannot be established with certainty". Esther: "we do not know who wrote the book". Job: Job himself did not write it, and its writer is unknown. Psalms: the headings "of David" can also mean "concerning" or "dedicated to". Proverbs: Solomon "was not the only author". Ecclesiastes: the writer's style and title "may point to another person and a later period". Lamentations: "anonymous and we cannot be certain who wrote it".
The books show other hands at work
The texts give their own evidence. Ruth ends by naming David as a famous descendant. So it was written once David was known, not in the days of the judges it describes. Even the NIV Study Bible says this makes Samuel an unlikely author. Joshua reports Joshua's death. Proverbs says some of its sayings were copied out by the men of King Hezekiah, about two and a half centuries after Solomon. It also gives whole chapters to Agur and to King Lemuel. The five books said to be Moses' own describe his death.
“And the women her neighbours gave it a name, saying, There is a son born to Naomi; and they called his name Obed: he is the father of Jesse, the father of David.”
“And it came to pass after these things, that Joshua the son of Nun, the servant of the Lord, died, being an hundred and ten years old.”
“These are also proverbs of Solomon, which the men of Hezekiah king of Judah copied out.”
“The words of Agur the son of Jakeh, even the prophecy: the man spake unto Ithiel, even unto Ithiel and Ucal,”
“The words of king Lemuel, the prophecy that his mother taught him.”
“So Moses the servant of the Lord died there in the land of Moab, according to the word of the Lord. And he buried him in a valley in the land of Moab, over against Beth–peor: but no man knoweth of his sepulchre unto this day. And Moses was an hundred and twenty years old when he died: his eye was not dim, nor his natural force abated. And the children of Israel wept for Moses in the plains of Moab thirty days: so the days of weeping and mourning for Moses were ended. And Joshua the son of Nun was full of the spirit of wisdom; for Moses had laid his hands upon him: and the children of Israel hearkened unto him, and did as the Lord commanded Moses. And there arose not a prophet since in Israel like unto Moses, whom the Lord knew face to face,”
This evangelical study Bible holds that Moses was the main author of the five books, but its introductions grant later hands. On Genesis it says some later editorial updating appears to be indicated, pointing to the notes on 14:14 and 36:31. On Numbers it says the book need not have come from Moses complete and in final form, that portions were probably added by later scribes or editors, and that the praise of Moses' humility in 12:3 would hardly convince if it came from his own mouth. On Deuteronomy it says the report of Moses' death in chapter 34 was almost certainly written by someone else.
This evangelical study Bible's introductions grant that many Old Testament books have no known author. Joshua: "we are unsure who the final author or editor was". Judges: authorship is "actually uncertain". Ruth: its writer is unknown, and the mention of David implies a later date than Samuel. 1-2 Samuel: who wrote them "cannot be known with certainty". 1-2 Kings: "little conclusive evidence" of who wrote them. Chronicles: the tradition that Ezra wrote it "cannot be established with certainty". Esther: "we do not know who wrote the book". Job: Job himself did not write it, and its writer is unknown. Psalms: the headings "of David" can also mean "concerning" or "dedicated to". Proverbs: Solomon "was not the only author". Ecclesiastes: the writer's style and title "may point to another person and a later period". Lamentations: "anonymous and we cannot be certain who wrote it".
Psalms: headings, not signatures
Only 73 of the 150 Psalms (the Hebrew songs and prayers) carry the heading "of David". The Hebrew phrase can also mean "concerning" or "dedicated to". The book's own note does not fit its headings. Psalm 72 ends with the note that the prayers of David are ended. Yet eighteen more psalms headed "of David" follow it, such as Psalm 86.
“The prayers of David the son of Jesse are ended.”
“A Prayer of David. Bow down thine ear, O Lord, hear me: for I am poor and needy.”
This evangelical study Bible's introductions grant that many Old Testament books have no known author. Joshua: "we are unsure who the final author or editor was". Judges: authorship is "actually uncertain". Ruth: its writer is unknown, and the mention of David implies a later date than Samuel. 1-2 Samuel: who wrote them "cannot be known with certainty". 1-2 Kings: "little conclusive evidence" of who wrote them. Chronicles: the tradition that Ezra wrote it "cannot be established with certainty". Esther: "we do not know who wrote the book". Job: Job himself did not write it, and its writer is unknown. Psalms: the headings "of David" can also mean "concerning" or "dedicated to". Proverbs: Solomon "was not the only author". Ecclesiastes: the writer's style and title "may point to another person and a later period". Lamentations: "anonymous and we cannot be certain who wrote it".
| Book | Credited to | What the evidence shows |
|---|---|---|
| Genesis to Deuteronomy | Moses | They report Moses' death and burial. |
| Ruth | Samuel | It ends by naming David, so it was written once David was known. Even a Christian study Bible says Samuel is unlikely to have written it. |
| Psalms | David | Only 73 of the 150 psalms carry the heading “of David”. Psalm 72 says the prayers of David are ended, yet more psalms headed “of David” follow it. |
| Proverbs | Solomon | Some of its sayings were copied out by King Hezekiah's men, about 250 years after Solomon. Whole chapters belong to Agur and to King Lemuel. |
A leading Christian study Bible also says nobody can be sure who wrote Joshua, Judges, Samuel, Kings, Esther, Job or Lamentations. So a Christian cannot say, book by book, which words came from the prophet whose name is on it.
A known Prophet and named scribes
The Qur'an says the Prophet (ﷺ) did not speak from his own desire. What he recited was revelation sent down to him. It came through one man whose life is recorded in detail. His scribes are known by name. One of them, Zayd ibn Thabit, gathered the Qur'an into one volume soon after his death. He used the written pieces and those who knew it by heart. Jeremiah, by contrast, warned that the false pen of the scribes had made the law a lie. The Qur'an says those given the Law changed words from their places. Yet Islam does not say every word in these books is lost. The Qur'an confirms the scripture that came before it, and we are told to judge by what Allah (﷾) has revealed (5:48).
“Nor does he say (aught) of (his own) Desire. It is no less than inspiration sent down to him:”
Zayd ibn Thabit reports that after many who knew the Qur'an by heart were killed at Yamama, Abu Bakr asked him to gather the Qur'an into one volume, reminding him that he used to write down the revelation for the Messenger of Allah. Zayd collected it from written pieces and from the memories of men, and the finished copy passed from Abu Bakr to Umar and then to Hafsa.
““ ‘How do you say, “We are wise, and Yahweh’s law is with us?” But, behold, the false pen of the scribes has made that a lie.”
“But because of their breach of their covenant, We cursed them, and made their hearts grow hard; they change the words from their (right) places and forget a good part of the message that was sent them, nor wilt thou cease to find them- barring a few - ever bent on (new) deceits: but forgive them, and overlook (their misdeeds): for Allah loveth those who are kind.”
“To thee We sent the Scripture in truth, confirming the scripture that came before it, and guarding it in safety: so judge between them by what Allah hath revealed, and follow not their vain desires, diverging from the Truth that hath come to thee. To each among you have we prescribed a law and an open way. If Allah had so willed, He would have made you a single people, but (His plan is) to test you in what He hath given you: so strive as in a race in all virtues. The goal of you all is to Allah; it is He that will show you the truth of the matters in which ye dispute;”
The Christian replies, and the answers
2 Peter 1:21 — Second Epistle of Peter, chapter 1, verse 21
“For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost.”
Cited for
It does not matter who held the pen. Holy men of God spoke as the Holy Spirit moved them, so God is the one speaking even where the man is unknown.
The response
Islam agrees that God (﷾) spoke through holy men. But the verse speaks of prophets. It does not tell a reader which books they wrote. The books themselves show other hands. Deuteronomy tells of the death of Moses. Proverbs says the men of Hezekiah copied out sayings of Solomon.
Where it lands — The verse speaks of prophets. It does not say which books they wrote, and the books show that other hands finished some of them.
Luke 24:44 — Gospel of Luke, chapter 24, verse 44
“And he said unto them, These are the words which I spake unto you, while I was yet with you, that all things must be fulfilled, which were written in the law of Moses, and in the prophets, and in the psalms, concerning me.”
Cited for
Jesus accepted the Law, the Prophets and the Psalms as scripture, so their authority does not depend on knowing who wrote each book.
The response
Jesus spoke of what was written in the law of Moses, the prophets and the psalms. He did not vouch for every later line in those books. That includes the death of Moses. It also includes the psalms placed after "The prayers of David the son of Jesse are ended". Jeremiah had already warned of "the false pen of the scribes".
Where it lands — Honouring the revelation given to the prophets is not the same as vouching for books finished by other hands.
Perspectives
Evangelical Christian
God inspired the Old Testament through human writers, and the Holy Spirit is its true author. Not knowing a writer's name does not make his book any less the word of God.
Peter says prophecy came not by the will of man. Holy men of God spoke as the Holy Spirit moved them.
Rebuttal
Islam agrees that God (﷾) spoke through holy men. But the verse describes prophets. It does not list the books they wrote. And the books show other hands at work, as when Deuteronomy tells of the death of Moses and Proverbs speaks of the men of Hezekiah.
Inspiration does not depend on knowing the human author's name.
Rebuttal
Granted, a name is not what makes a book scripture. But the Qur'an says who received the revelation: Allah (﷾) gave the Zabur to David (4:163). Psalm 72 ends by saying David's prayers are ended, yet eighteen psalms headed "of David" follow it.
The Islamic perspective
Allah (﷾) sent prophets with scripture. But for much of the Old Testament, even Christian scholars cannot say who wrote it, and other hands finished some books. The Qur'an confirms what is true in them (5:48). It came through one known Prophet (ﷺ) and was written down by named scribes.
An evangelical study Bible lists books whose authors are unknown or uncertain. They are Joshua, Judges, Ruth, Samuel, Kings, Esther, Job and Lamentations.
Joshua reports Joshua's death, and Proverbs names Hezekiah's men, Agur and Lemuel as sources. So these books were finished by other and later hands than the men tradition names (Joshua and Solomon).
Ruth names David as a known figure, which points to a later date than Samuel, the man tradition names. The NIV Study Bible says so itself.
Eighteen psalms headed "of David" come after the note that David's prayers are ended. So the book's own note and its contents do not agree.
The Qur'an says Allah (﷾) gave David the Zabur (the Psalms). The Book of Psalms as it stands is not that revelation kept whole: its own note ends David's prayers at Psalm 72, yet more follow.
The Qur'an came through one known Prophet (ﷺ) as revelation, and was written down by his scribes.