Short answer
To keep the recitation united, and to stop partial private copies being taken as the standard text. Less than twenty years after the Prophet (ﷺ) died, Muslims in Syria and Iraq argued over how the Qur'an was recited. The companion Hudhayfah, one of the people who knew the Prophet (ﷺ), warned the caliph (ruler of the Muslims) Uthman to act. He feared Muslims would differ over their Book as Jews and Christians had. Uthman had copies made from the volume kept by Hafsah, the Prophet's (ﷺ) widow. That volume had been gathered soon after the Prophet's (ﷺ) death. He sent a copy to every province. Then he ordered the other written copies burned. It was done openly, while many who had heard the Qur'an from the Prophet (ﷺ) were alive. Ali, the next caliph, said Uthman had acted only after consulting the companions.
Full explanation
What happened
Sahih al-Bukhari is a collection of hadith, the reports of what the Prophet (ﷺ) said and did. It gives the account. Hudhayfah saw Muslim armies from Syria and Iraq quarrelling over the recitation, and went to Uthman. Uthman borrowed Hafsah's volume. He had the Prophet's (ﷺ) scribe Zayd ibn Thabit and three men of Quraysh copy it. Then he returned it to her, sent the copies out, and ordered the other written material burned. He told the copyists that where they differed they should write in the dialect of Quraysh, the tribe of Mecca, in which it was revealed.
Anas reports that Hudhayfa ibn al-Yaman, alarmed at how the soldiers of Syria and Iraq differed in reciting the Qur'an, urged Uthman to save the community before it differed over its Book as the Jews and Christians had. Uthman borrowed the collected sheets kept by Hafsa, had Zayd ibn Thabit and three men of Quraysh copy them, telling the three that wherever they differed with Zayd they should write in the dialect of Quraysh, in which the Qur'an was revealed, returned the sheets to her, sent a copy to every province, and ordered all other written Qur'anic material to be burned.
Where Uthman's text came from
Uthman did not write a new Qur'an. He copied the volume that Zayd ibn Thabit had gathered for Abu Bakr, the first caliph. That was within two years of the Prophet's (ﷺ) death. Zayd gathered it from written pieces and from the men who knew it by heart. The Prophet (ﷺ) had also gone over the Qur'an with the angel Gabriel every year, and twice in his last year.
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.
Abu Hurayra reports that Gabriel went over the Qur'an with the Prophet (ﷺ) once every year, and twice in the year he died.
- Every year
Gone over with Gabriel
The Prophet (ﷺ) went over the Qur'an with the angel Gabriel every year, and twice in his last year.
- Within two years of his death
Gathered for Abu Bakr
Zayd ibn Thabit gathered it into one volume, from written pieces and from those who knew it by heart. Hafsah later kept it.
- Less than twenty years after
A copy for every province
Hudhayfah warned of quarrels over the recitation. Zayd and three men of Quraysh copied Hafsah's volume, and a copy went to each province.
- Then
Private copies withdrawn
The companions' private copies, whole or in pieces, were destroyed so that one agreed text stayed in use. Ali later said Uthman acted only after consulting the companions.
What was burned, and who agreed
What was burned was not a rival Qur'an. It was the companions' own copies, whole or in pieces. They were written for private use. Ali became caliph after Uthman, and he defended what Uthman had done. He said Uthman acted only after consulting the companions, and that had he been in charge he would have done the same. The Prophet (ﷺ) had died less than twenty years before. So many who had heard the Qur'an from him were alive to object.
Suwayd ibn Ghafala reports that Ali said to speak only good of Uthman about the copies of the Qur'an, because he acted only after consulting the Companions, and that had Ali been in charge he would have done the same. Ibn Hajar calls the chain of this report sound.
Anas reports that Hudhayfa ibn al-Yaman, alarmed at how the soldiers of Syria and Iraq differed in reciting the Qur'an, urged Uthman to save the community before it differed over its Book as the Jews and Christians had. Uthman borrowed the collected sheets kept by Hafsa, had Zayd ibn Thabit and three men of Quraysh copy them, telling the three that wherever they differed with Zayd they should write in the dialect of Quraysh, in which the Qur'an was revealed, returned the sheets to her, sent a copy to every province, and ordered all other written Qur'anic material to be burned.
A companion's text found in Sanaa
A manuscript found in Sanaa, the capital of Yemen, has an older text, erased and written over. The scholars who edited it argue that it comes from a companion's codex (a copy in book form). Copies of that kind existed before Uthman's. Its differences from the standard text are mostly small variants in words and phrases within the same verses. It also puts some suras (chapters) in a different order. If the editors are right, it shows the kind of copy Uthman withdrew. It is not a different Qur'an.
An edition and study of the Sanaa 1 lower text. Its differences from the standard text are mostly small variants in words and phrases, of the kind the early sources report for the companions' own codices. Within each sura the surviving lower text has the same verses as the standard text, in the same order, with two exceptions: verses 20:31-32 are swapped, and verse 9:85 (which almost repeats 9:55) is missing. The order of the suras differs.
A contrast with the Bible's list of books
Uthman's copies were sent out less than twenty years after the Prophet (ﷺ) died, while many who had learned the Qur'an from him were alive. The earliest surviving list of exactly the twenty-seven books of the New Testament comes from Athanasius, a church bishop, in 367. That is more than three centuries after Jesus.
Athanasius, bishop of Alexandria, lists the books he counts as scripture. His New Testament list is the twenty-seven books of today's New Testament, the earliest surviving list of exactly these books and no others.
The critics' claims
Sahih al-Bukhari 4987 — Kitab Fada'il al-Qur'an (Virtues of the Qur'an), hadith 4987
Anas reports that Hudhayfa ibn al-Yaman, alarmed at how the soldiers of Syria and Iraq differed in reciting the Qur'an, urged Uthman to save the community before it differed over its Book as the Jews and Christians had. Uthman borrowed the collected sheets kept by Hafsa, had Zayd ibn Thabit and three men of Quraysh copy them, telling the three that wherever they differed with Zayd they should write in the dialect of Quraysh, in which the Qur'an was revealed, returned the sheets to her, sent a copy to every province, and ordered all other written Qur'anic material to be burned.
Cited for
Uthman burned the other copies to suppress different versions of the Qur'an, so we cannot know what the original said.
The response
The same report says where Uthman's text came from: the volume already gathered under Abu Bakr from writing and memory. Many companions also held the Qur'an in memory, having learned it from the Prophet (ﷺ). So a changed text would have been noticed at once. Ali, the next caliph, defended the decision. And the Sanaa lower text, which its editors identify as a companion's codex, differs mainly in small wording within the same verses. It also puts some suras in a different order.
Where it lands — The burning removed private copies, not a lost Qur'an. The text Uthman sent out is the one the Prophet's (ﷺ) companions already knew.
Jami al-Tirmidhi 3104 — Abwab Tafsir al-Qur'an (Chapters on the Interpretation of the Qur'an), hadith 3104
Anas gives the account of Hudhayfah's warning and Uthman's copies. Al-Zuhri adds that Abdullah ibn Mas'ud disliked Zayd ibn Thabit being given the copying instead of him, and told the people of Iraq to keep their own copies. Al-Zuhri adds that it reached him that some of the most virtuous companions disliked Ibn Mas'ud's view.
Cited for
Ibn Mas'ud, a leading companion, objected to Uthman's copy, so the companions did not agree.
The response
In this report, Ibn Mas'ud's complaint is that Zayd ibn Thabit, a younger man, was given the copying instead of him. He does not say the text was wrong. He told the people of Iraq to keep their own copies, but he names no verse that Uthman's copy left out or changed. Al-Zuhri, an early eighth-century Muslim scholar who narrates the report, adds that he was told some of the most virtuous companions disliked his view. Ali, the next caliph, defended what Uthman did and said he would have done the same.
Where it lands — In this report, Ibn Mas'ud's complaint is about who did the copying. He names no verse that Uthman's copy left out or changed.
Sahih al-Bukhari 4992 — Kitab Fada'il al-Qur'an (Virtues of the Qur'an), hadith 4992
Umar heard Hisham ibn Hakim recite Surat al-Furqan differently from the way he had learned it and brought him to the Prophet (ﷺ). The Prophet had each recite, said of both readings that the surah was revealed that way, and said the Qur'an was revealed to be recited in seven ways, so recite whichever is easier.
Cited for
The Qur'an was revealed in seven modes, and Uthman kept one and burned the rest.
The response
The Prophet (ﷺ) said the Qur'an was revealed in seven ahruf (modes of recitation), as an ease for tribes who spoke differently. He told his companions to recite whichever mode was easier, so reciting in one mode was always allowed. Uthman told his copyists that where they differed they should write in the dialect of Quraysh. Scholars differ on how the seven modes relate to the readings recited today, such as Hafs and Warsh. Those readings all fit Uthman's written text. They differ in some vowel sounds and in a few words. They never contradict each other about God (﷾), the prophets or the Hereafter (life after death).
Where it lands — The seven modes were an allowance for ease, taught by the Prophet (ﷺ) himself, and no one was ever required to recite them all. Nothing of the message was lost. The readings recited today differ in sound and a few words, not in teaching about God (﷾), the prophets or the Hereafter.
Perspectives
Christian critics
Some Christian apologists argue that Uthman chose one version of the Qur'an and destroyed the rest. So, they say, no one can know what was lost.
Uthman ordered all other written Qur'anic material, fragments or whole copies, to be burned.
Rebuttal
The report is true: Uthman did order the other written material burned. But what went were the companions' own private copies, some of them partial. His text was copied from the volume gathered under Abu Bakr, and Ali, the next caliph, defended what he did.
The burning shows that different Qur'ans existed and that one was imposed.
Rebuttal
Many companions knew the Qur'an by heart from the Prophet (ﷺ), so a changed text would have been noticed at once. The Sanaa lower text, which its editors identify as a companion's codex, differs mainly in small wording and in the order of some suras. It is not a different Qur'an, and Ali, the next caliph, defended what Uthman did.
The Islamic perspective
Uthman protected a text that already existed. He copied the volume gathered under Abu Bakr, sent it to every province, and removed private copies so that the recitation would not drift apart. Ali said Uthman acted only after consulting the companions of the Prophet (ﷺ).
Hudhayfah's warning was that Muslims would differ over their Book as the Jews and Christians had.
Uthman's copies were made from Hafsah's volume, gathered from writing and memory within two years of the Prophet's (ﷺ) death.
Ali said Uthman acted only after consulting the companions and that he would have done the same.
The Sanaa lower text, which its editors identify as a companion's codex, differs from the standard text. The differences are small variants of words and phrases, and the order of some suras.