The Messenger of Allah ﷺ used to pray eleven rak'ahs (at night, observing the witr with one rak'ahs). When he finished it (the prayer), he would lie down on his right side. (Using translation from Abū Dāʾūd 1335)
أَنَّ النَّبِيَّ ﷺ كَانَ يُصَلِّي مِنَ اللَّيْلِ إِحْدَى عَشْرَةَ رَكْعَةً يُوتِرُ مِنْهَا بِوَاحِدَةٍ فَإِذَا فَرَغَ مِنْ صَلَاتِهِ اضْطَجَعَ عَلَى شِقِّهِ الْأَيْمَنِ