The Messenger of Allah ﷺ used to pray nine rakahs during the night.
أخبرنا هناد بن السري عن أبي الأحوص عن الأعمش أراه عن إبراهيم عن الأسود
كان رسول الله ﷺ يصلي من الليل تسع ركعات
[Sahih] Reported by Tirmidhi, Prayer, a chapter on this topic, no. 443, from Hannad with the same wording, and he said, hasan [sahih] gharib. It is also found in Kubra, no. 427, and it has corroborating narrations in Muslim, Travelers' Prayer, the chapter on the permissibility of voluntary prayer standing or sitting... etc, no. 730, and elsewhere.