سنن النسائي

It was narrated that Sa'd bin Hisham said: "I said: 'O Mother of the believers! Tell me about the Witr of the Messenger of Allah (ﷺ).' She said: 'We used to prepare his siwak and water for purification, then Allah (SWT) would wake him when He willed to wake him at night. He would use the siwak and perform wudu, then pray eith rak'ahs; not sitting until the eighth rak'ah, when he would sit and remember Allah (SWT) and call upon Him. Then he would say the taslim loud enough for us to hear.'"