Qur'an was well documented and committed to memory during the time of revelation. When it was revealed prophet Muhammad (pbuh) memorised it and commanded the scribes of revelation to record it and they did. He also used to command his companions to commit it to memory. The Qur'an was, at intervals, revealed by Allah to prophet Muhammad (pbuh) through the angel Gabriel, who used to revise the Qur'an with prophet Muhammad once a year but the year the prophet died, the revision was only made twice. When any part of the Qur'an was revealed, the prophet would tell the scribes where to place it. In other words, it was also revealed to prophet Muhammad how to arrange the verses and how to arrange the Surahs (chapters), and then he conveyed this to the scribes.
Since paper manufacture was only discovered relatively recently, the materials the scribes used in the old days to record the revelations and history, varied. Some used stones; many discoveries were carved on stones, whereas some used leather and so on. Various other materials like parchment and bones were also used to record the Qur'an.
When Prophet Muhammad (pbuh) died, the whole Qur’an was memorized and written down but not in one volume.
Collecting the Quran
The First Step
Abu Baker was the first Muslim Caliph. A Caliph was a Muslim ruler. After the demise of prophet Muhammad (pbuh) he was nominated to be the leader of Muslims. During his reign, Islam was targeted and many hufaz (people knowing the Qur’an by heart) were martyred. In Muslim history, it is narrated that over seventy hufaz were martyred in one event called the ‘Ahlulyamamah’.
Omar Ibn Al-Khattab went to the Muslim Caliph, Abu Bakr, and expressed his concerns about the preservation of the Qur’an to him. He suggested that the Qur’anic records would be collected in one place. So Abu Bakr commissioned a group of the prophet’s companions headed by Zaib Ibn Thabit, a companion of prophet Muhammad and one of the scribes of the Quran, to collect the Quranic records. These records were then kept with Abu Bakr and after his death Omar Ibn Al-Khattab, the second Muslim Caliph, preserved them and they were kept afterwards with Hafsa, the prophet’s wife.
How did Zaid Ibn Thabit collect the Qur’an?
He depended on two sources:
1. Oral Source: Many people memorised the Qur’an by heart during the lifetime of prophet Muhammad (pbuh). Muslims believe firmly that there is a great reward, in the hereafter, for memorising the Qur’an. Again Muslims believe that the Qur’an is Allah’s word and reciting it is an act of worship. This urged Muslims to recite frequently. Bearing in mind that Zaid himself was one of the hufaz, he collected the Qur’an from the hearts of groups and not individuals. Members of these groups had to recite the same words by heart in order to be considered trustworthy.
2. Written Source: Zaid collected what was proved authentic, to be recorded. To make sure that it was done in this way, Zaid did not accept any writings unless two just people bore witness that they were written before prophet Muhammad (pbuh). It is narrated that Abu Bakr commanded Omar and Zaid to sit at the gate of the mosque and record only what was verified by two witnesses.
The Second Step
During the era of the second and third Muslim Caliphs, Islam had expanded and many people from different countries embraced Islam. Some of the new Muslims were non-Arabs and it was not easy for them to read the Qur’an because it was in Arabic. But the Qur’an is one of the main sources of Islam. There was no other alternative but to learn the Qur’an, so Muslim Caliphs sent the prophet’s companions to teach them the Qur’an. But this did not solve the problem. People read the Qur’an in various ways but the proper intonation is very important. When Othman, the third Muslim Caliph, heard about this, he called for a meeting. The companions of prophet Muhammad assembled and discussed the issue. They reached a consensus and agreed to make copies of the Qur’anic records collected by Zaid Ibn Thabit in the reign of the first Muslim Caliph, Abu Bakr and send them all over the Muslim countries.
How did Othman do this?
He nominated four of the prophet’s companions who were hufaz to do this job.
1 Zaid Ibn Thabit: He was from Medina and he was the one that Abu Bakr, the first Muslim caliph, nominated to collect the Qur'an. He is one of the scribes of the Qur'an. He died in 45 Hj.
2 Abdullah Ibn Al-Zubair died in 73 Hj.
3 Sa’id Ibn AL-Aas died in 58 Hj.
4 Abdulrahman Ibn Al-Harith died in 43 Hj.
In fulfilling this job they used a very accurate method based on the Qur’anic Records, collected during the era of the first Muslim Caliph, Abu Bakr as the main source.
This was done under the supervision of Othman Ibn Affan, the third Muslim Caliph and the most eminent figures of the companions of prophet Muhammad (pbuh). Many copies were made and sent to different Muslim places. Not only this, but with every copy one of the companions of the prophet was sent to teach people the correct recitation of the Glorious Qur’an.
Conclusion
In summary, the Quran passed through three phases:
1 Recording it during the time of revelation
2 Collecting the Qur’anic Records during the era of the First Muslim Caliph, Abu Bakr
3 Making copies of the Qur’anic records.
In the first stage the Qur’an was written on different materials e.g. bones and parchment.
In the second stage Abu Bakr, the first Muslim Caliph, collected all the Qur’anic records.
In the third stage Othman Ibn Affan, the third Muslim Caliph, copied all the Quranic records collected by Abu Bakr in one book and made many copies of them.
The unquestioned authenticity of the Qur’an and its contents can be proven through history, as explained shortly above. The fact that the Qur’an, which was revealed 1400 years ago is still intact and upheld is also confirmation of its truth. Another important fact is the consistency of the Qur'an - all Muslims all over the word have the same Qur’an. There is no variance in its translation. If you take a copy of the Qur’an, open any chapter, select any verse and choose any word, then travel to any part of the world, and open the same chapter and the same verse and the same word, you will find that it is the same. As well as this, there are no paradoxes in the Qur’an. @Aeronaut @Xeric 
