Abdullah bin Mubarak عبد الله بن المبارك · The Book on Al-Witr

Umm Sulaim came upon the Prophet and said: "Teach me some words that I can say in my Salat." So he said: "Mention Allah's Greatness (saying: Allahu Akbar) ten times, mention Allah's Glory (saying: Subhan Allah) ten times, and mention Allah's praise (saying: Al-Hamdulilah) ten times. Then ask as you like, (for which) He says: 'Yes. Yes.'"