The Messenger of Allah ﷺ used to pray eleven units of prayer. That was his prayer, meaning at night. He would prostrate for as long as it takes one of you to recite fifty verses before raising his head. Then he would pray two units before the dawn prayer, after which he would lie down on his right side until the caller to prayer came to summon him for the prayer.
كان رسول الله ﷺ يصلي إحدى عشرة ركعة. كانت تلك صلاته- تعني بالليل- فيسجد السجدة من ذلك قدر ما يقرأ أحدكم خمسين آية قبل أن يرفع رأسه ويركع ركعتين قبل صلاة الفجر، ثم يضطجع على شقه الأيمن حتى يأتيه المؤذن للصلاة.
Bukhari reported it in the Book of Witr (994) and Muslim in the Book of the Prayer of Travelers (736), both through Zuhri, from Urwa, from Ayesha, and he mentioned it, and the wording is Bukhari's.