سنن ابن ماجه

It was narrated that Zaid bin Khalid Al-Juhani said: “I said, I must observe how the Messenger of Allah (ﷺ) prays tonight. So I lay down at his door. The Messenger of Allah (ﷺ) got up and prayed two brief Rak’ah, then two long ones, which were very, very long, then two Rak’ah which were shorter than the ones preceding them, then two Rak’ah which were shorter than the ones preceding them, then two Rak’ah which were shorter than the ones preceding them, then two Rak’ah, then Witr. That was thirteen Rak’ah.”