Sunan Abi Dawud 1478
سنن أبي داود#1478SahihUbayy b. Ka'b said:The Prophet (ﷺ) was present at the pool of Banu Ghifar, Gabriel came to him and said: "Allah has commanded you to make your community read (the Qur'an) in one harf. He (the Prophet) said: 'I beg Allah His pardon and forgiveness; my community has not strength to do so'. He then came for the second time and told him the same thing till he reached up to seven harfs. Finally, he said: 'Allah has commanded you to make your community read (the Qur'an) in seven harfs; in whichever mode they read, that will be correct
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Muhyi Al-Din Abdul HamidSahih
Shuaib Al ArnautSahih
Zubair Ali ZaiSahih Muslim (821)
In-book reference: 8:63