The Prophet ﷺ used to pray eleven rak'ahs at night, ending them with one rak'ah of witr, then he would lie down on his right side. (Using translation from Nasāʾī 1696)
أَنَّ النَّبِيَّ ﷺ كَانَ «يُصَلِّي مِنَ اللَّيْلِ إِحْدَى عَشْرَةَ رَكْعَةً يُوتِرُ مِنْهَا بِوَاحِدَةٍ ثُمَّ يَضْطَجِعُ عَلَى شِقِّهِ الْأَيْمَنِ»