Saad bin Hisham reported,

I said, "Umm Muiminin, tell me about the witr prayer of the Messenger of Allah ﷺ."She replied, "We used to prepare his tooth-stick and his water for purification, and Allah would rouse him whenever He willed to rouse him during the night. He would brush his teeth, perform ablution, and pray eight rakahs, not sitting during them except at the eighth. Then he would sit, remember Allah , and supplicate. After that, he would give the closing salutation in a way that we could hear."

أخبرنا محمد بن بشار قال حدثنا يحيى عن سعيد عن قتادة عن زرارة بن أوفى

عن سعد بن هشام قال

قلت يا أم المؤمنين أنبئيني عن وتر رسول الله ﷺ قالت كنا نعد له سواكه وطهوره فيبعثه الله لما شاء أن يبعثه من الليل فيتسوك ويتوضأ ويصلي ثمان ركعات لا يجلس فيهن إلا عند الثامنة فيجلس فيذكر الله عز وجل ويدعو ثم يسلم تسليما يسمعنا