Abu Salamah (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) would pray two rak'ahs after the witr, reciting in them while sitting; when he (peace and blessings be upon him) intended to bow, he would stand up.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4819