Urwah bin al-Zubayr (may Allah have mercy on him) narrates from Sayyidah Aishah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) used to pray thirteen rak'ahs: two rak'ahs before the Fajr prayer, six rak'ahs two by two, and five witr; he did not sit between them, sitting only in the last rak'ah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4802