Sahih Muslim, 1804

Zaid b Khalid al-Juhani said:I would definitely watch at night the prayer observed by the Messenger of Allah (ﷺ). He prayed two short rak'ahs, then two long, long, long rak'ahs, then he prayed two rak'ahs which were shorter than the two preceding rak'ahs, then he prayed two rak'ahs which were shorter than the two preceding, then he prayed two rak'ahs which were shorter than the two preceding, then observed a single one (Witr), making a total of thirteen rak'ahs

Rapporté par Zayd ibn Khalid al-Juhani رضي الله عنه : J’ai voulu observer la prière de nuit du Messager d’Allah ﷺ. Il a prié deux rak‘as courtes, puis deux rak‘as très longues, puis deux rak‘as un peu plus courtes que les précédentes, puis encore deux rak‘as plus courtes, puis encore deux rak‘as plus courtes, puis il a terminé par une rak‘a (le Witr), ce qui fait un total de treize rak‘as