Sahih Muslim 1086
صحيح مسلم#1086SahihA'isha reported that the Messenger of Allah (ﷺ) before his death recited often:Hallowed be Thou, and with Thy praise, I seek forgiveness from Thee and return to Thee. She reported: I said: Messenger of Allah, what are these words that I find you reciting? He said: There has been made a sign for me in my Ummah; when I saw that, I uttered them (these words of glorification for Allah), and the sign is:" When Allah's help and victory..... to the end of the surah
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 4:248