Sa'd bin Hisham (may Allah have mercy on him) narrates: I asked the Mother of the Believers, Sayyidah Aishah (may Allah be pleased with her), about the night prayer (tahajjud) of the Prophet (peace and blessings be upon him), and she said: "His water for ablution and his tooth-stick (miswak) would be set out for him (peace and blessings be upon him); then Allah Almighty would wake him (peace and blessings be upon him) whenever He willed during the night. He (peace and blessings be upon him) would use the tooth-stick and perform ablution, then stand for prayer and offer nine rak'ahs, and he would pray two rak'ahs sitting. And when he (peace and blessings be upon him) was ill or could not get up at night (for some reason), he would offer twelve rak'ahs."
Hadith Referenceالمعجم الأوسط / باب العين / 4404
Hadith Takhrij«أخرجه أبو داود فى «سننه» برقم: 56، والطبراني فى «الأوسط» برقم: 502»