سنن النسائي

It was narrated that 'Asim bin Humaid said: "I asked 'Aishah with what the Messenger of Allah (ﷺ) [SAW] would start Qiyam Al-Lail. She said: 'You have asked me about something that no one else has asked me about. He used to say Allahu Akbar ten times, and Subhan-Allah ten times, and Istaghfir-Allah ten times, and he would say, Allahummaghfirli, wahdini, warzuqni, wa'afini (O Allah, forgive me, guide me, grant me provision and give me good health,) and he would seek refuge from the difficulty of the standing on the Day of Resurrection.'"