Quran was compiled during the era of Prophet Sallallahu alyhi wasallam, we find score of companions of Prophet Sallallahu alyhi wasallam including four Caliphs, Zaid bin Sabit, Muaaviya bin Abi Sufyan, Mugheerah bin Shu’bah, Zubair bin Awam, Ubay bin Ka’b, Amr bin Aas etc. RaziAllahu anhum (See Fathul Bari: V . 9, Zadul Maad: V. 1.p30) were assigned to record every single verse of holy book as soon as it was revealed.
Yes there was shortage of paper, so they used bones, pieces of leather, clothes, leaves of trees, and sometimes pieces of paper.
Every Muslim, even a new one, was supposed to memorize a sizeable part of Quran, actually it was rather an obligation and a duty to learn, memorize, preserve the Quran and teach it to their kindreds, let alone the companions living in Madina all the time. Plenty of them have memorized it from beginning to end, recited in prayers, listened from Prophet in Salah.
If it was not composed during the lifetime of Prophet Sallallahu alyhi wasallam, then why he ordered his companions not to travel with Quran to the land of enemy? (Sahi Bukhari V.1 p.418) and Why it was called “Alkitab” (compiled book)?
Then we find the Caliph Abu Bakar RaziAllahu Anhu, commanding Zaid bin Sabit along with Umar bin Khattab Razi Allahu Anhuma to collect every single piece of Quran written in front of Prophet Sallallahu alyhi wasallam, every person who brings any verse was asked to substantiate his claim with the testimony of at least two persons who saw that particular verse composed under the eyes of Prophet Sallallahu alyhi wasallam.
The Quranic verses were such a common scenario among Muslims at that time, even a child could distinguish the Quranic verses from other sorts of speech. So it’s ironical to claim that Hazrat Zaid Raziallahu Anhu and his team compiled the Quran with no proper verification or authentication from Prophet Sallallahu alyhi wasallam.
Moreover, Hazrat Zaid Raziallahu Anhu was among the ones appointed by Prophet Sallallahu alyhi wasallam himself to register the divine revelation, it is understood that he would possess the Quran in complete written form, this argument is strengthened by the narration of Hazrat Ana’s Raziallahu Anhu, he said once the tribes of Aws and Khazraj (two prime tribes of Madina) competed to count their services for Islam, on that occasion Khazraj prided on having four persons who memorized the entire Quran in front of Prophet Sallallahu alyhi wasallam (Fathul Bari V.9.P 41-42).
That’s why Hazrat Zaid Raziallahu Anhu had been trusted by Caliph Abu Bakr Raziallahu Anhu to supervise the compilation once again because he was much qualified and experienced for the job, his eligibility was confirmed by Prophet Sallallahu alyhi wasallam himself.
The intention was rather to follow the footprint of Prophet Sallallahu alyhi wasallam even in composition of Quran, there was no one to raise a finger at the expertise of Zaid bin Sabit Raziallahu Anhu in this regard, especially when he got the full assistance and guidance of likes of Hazrat Umar and Abu Bakr Raziallahu Anhuma.