Musnad Ahmad 3247

It was narrated from Muhammad bin 'Ali, from his father, from his grandfather, from The Prophet (ﷺ), that he got up at night and cleaned his teeth, then he prayed two rak'ahs, then he slept. Then he got up, cleaned his teeth and did wudoo’, then he prayed two rak'ahs, until he had prayed six, then he prayed Witr with three, and he prayed two rak'ahs.