He observed thirteen rak'ahs (in the night prayer). He observed eight rak'ahs and would then observe Witr and then observe two rak'ahs sitting, and when he wanted to bow he stood up and then bowed down, and then observed two rak'ahs in between the Adhan and lqama of the dawn prayer. (Using translation from Muslim 738b)
عَنْ صَلَاةِ رَسُولِ اللهِ ﷺ؟ فَقَالَتْ كَانَ «يُصَلِّي ثَمَانِ رَكَعَاتٍ ثُمَّ يُوتِرُ ثُمَّ يُصَلِّي رَكْعَتَيْنِ وَهُوَ جَالِسٌ فَيَقْرَأُ وَيَرْكَعُ وَيُصَلِّي رَكْعَتَيْنِ بَيْنَ النِّدَاءِ وَالْإِقَامَةِ مِنْ صَلَاةِ الصُّبْحِ» تَابَعَهُ جَعْفَرُ بْنُ رَبِيعَةَ