Hisham bin Urwah narrates from his father that Aishah (may Allah be pleased with her) said: His (peace and blessings be upon him) prayer at night was thirteen rak'ahs. He (peace and blessings be upon him) would pray five rak'ahs of witr without saying the salam in them; then he would sit in the last rak'ah and say the salam.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4799