From Sahih Muslim (Hadith 1086):
A'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
Reference: Muslim 1086