Sunan an-Nasa'i 509
سنن النسائي#509SahihIt was narrated that Abu Bakr bin 'Uthman bin Sahl bin Hunaif said:"I heard Abu Umamah bin Sahl say: 'We prayed Zuhr with 'Umar bin 'Abdul-'Aziz, then we went out and entered upon Anas bin Malik, and we found him praying 'Asr.'" I said: "O uncle, what is this prayer that you prayed?" He said: "'Asr; this is the prayer of the Messenger of Allah (ﷺ) that we used to pray with him
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 6:16