It wasnarrated that 'Asim bin Humaid said:
"I asked 'Aishah: 'Withwhat did the Prophet (ﷺ) start voluntary prayers?' She said: 'Youhave asked me about something which no one has asked before. He usedto say Allahu Akbar ten times, and Al-Hamdu Lillah ten times andSubhan Allah ten times, and he would say Allahumma aghfirli wahdini,warzuqni, wa 'afini (O Allah, forgive me, guide me, grant meprovisionand give me good health)," and he would seek refuge fromthedifficulty of the standing on the Day of Resurrection."
English reference: Vol. 1, Book 5, Hadith 1356
Arabic reference: Book 5, Hadith 1418