as Salam Alaykum.
Hafiz ibn Kasir in his “Fadhail al-Quran” (p 44, Darul Itisam, Turkey) said:
“Like it was reported by imams like Waki (ibn al-Jarrah), (Abdurrahman) ibn al-Mahdi and Kabisa, Ali ibn Abi Talib (radi Allahu anh said):
The one who got greatest reward in regard to scrolls of Quran is Abu Bakr! The one who first gathered Quran between two covers was Abu Bakr”.
(Ibn Kasir said) – The chain of this report is sound”.