I said, "Umm Muiminin (Ayesha), tell me about the witr prayer of the Messenger of Allah ﷺ."She replied, "We would prepare his toothstick and his water for purification, and Allah would rouse him whenever He willed during the night. He would then use the toothstick, perform ablution, and pray nine rakahs, sitting only in the eighth..." and she narrated the hadith in full.
قلت يا أم المؤمنين (عائشة) أنبئيني عن وتر رسول الله ﷺ فقالت: كنا نعد له سواكه وطهوره، فيبعثه الله ما شاء أن يبعثه من الليل، فيتسوك، ويتوضأ، ويصلي تسع ركعات لا يجلس فيها إلا في الثامنة… الحديث بطوله.
Reported by Muslim in "Prayer of the Traveler" (746) from the hadith of Qatada, from Zurara, from Saad bin Hisham bin Amir, who related it in a long hadith that has already been mentioned in the chapter on the Prophet's ﷺ night prayer.