Sheikh `Abdul-Majeed Subh, a prominent Azharite scholar, answers: “The Glorious Qur’an was revealed gradually within a period of 23 years of Prophet Muhammad’s (peace and blessings be upon him) outstanding life. The Prophet (peace and blessings be upon him) ordered his Companions to observe the order of the Qur’anic surahs. `Uthmaan Ibn `Affaan (may Allah be pleased with him) narrated: “Sometimes, several surahs were revealed to Prophet Muhammad (peace and blessings be upon him). When anything was revealed to him, he would call on one of his scribes and say: ‘Insert this into the surahs where there is such and such.’ When some verses were revealed, he would say: ‘Insert these verses into the surahs in which there is such and such.’ When a single verse was revealed, he would say: ‘Insert this verse into the surahs in which there is such and such.’” (Reported by Ahmad, Abu Dawud, and At-Tirmidhi)
There is another Hadith that is more worthy-mentioning here. It reads: “Allah’s Messenger (peace and blessings be upon him) told `Uthman Ibn Abu Al-`As: ‘Jibril (Gabriel) (peace and blessings be upon him) came (to me) and ordered me to insert this verse into this position of these surahs. The verse reads: ‘Lo! Allah enjoineth justice and kindness, and giving to kinsfolk, and forbiddeth lewdness and abomination and wickedness. He exhorteth you in order that ye may take heed’.(An-Nahl: 90)” (Reported by Imam Ahmad)
The Prophet (peace and blessings be upon him) recited the Glorious Qur’an before his honourable Companions in this very order. Consequently, the Companions committed it to their hearts in this order. Arch-angel Gabriel (peace be upon him) used to recite the Qur’an before Prophet Muhammad (peace and blessings be upon him) once a year and twice at the year of his death.
Muslim scholars have unanimously agreed on that the arrangement of every verse in the Qur’an is tawqifi (i.e. something that has come to us from Almighty Allah through Divine revelation) and is not left to humans or even Prophet Muhammad (peace and blessings be upon him) to decide. This is applicable to the order of surahs in the copy of the Glorious Qur’an. Consequently, the majority of scholars consider it makruh (detestable act) to recite the Qur’an starting from the final-positioned surahs.
Historically speaking, Abu Bakr As-Siddiq (may Allah be pleased with him) was the one who actually collected all surahs of the Qur’an into one mus-haf (book compiling all the scripts of the various surahs of the Qur’an). Afterwards, `Uthman Ibn `Affan (may Allah be pleased with him) made more than one copy of what has been collected by Abu Bakr and sent them all over the Islamic territories. Thus, arranging the Glorious Qur’an has been done during the lifetime of Prophet Muhammad (peace and blessings be upon him) and during the Rightly-guided Caliphs’ eras while thousands of Companions were still alive and witnessing the whole issue (nothing was reported to indicate the rejection of anyone of them to the issue).”