Messenger of Allah ﷺ used to offer eleven rakʿat and that was his prayer. He used to prolong the prostration to such an extent that one could recite fifty verses (of the Qur'an) before he would lift his head. He used to pray two rakʿat (Sunna) before the Fajr prayer and then used to lie down on his right side till the call-maker came and informed him about the prayer.  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ يُصَلِّي إِحْدَى عَشْرَةَ رَكْعَةً كَانَتْ تِلْكَ صَلاَتَهُ يَسْجُدُ السَّجْدَةَ مِنْ ذَلِكَ قَدْرَ مَا يَقْرَأُ أَحَدُكُمْ خَمْسِينَ آيَةً قَبْلَ أَنْ يَرْفَعَ رَأْسَهُ وَيَرْكَعُ رَكْعَتَيْنِ قَبْلَ صَلاَةِ الْفَجْرِ ثُمَّ يَضْطَجِعُ عَلَى شِقِّهِ الأَيْمَنِ حَتَّى يَأْتِيَهُ الْمُنَادِي لِلصَّلاَةِ