Lady Aisha (may Allah be pleased with her) narrates that the Messenger of Allah (peace and blessings be upon him) used to pray nine rak'ahs (units of prayer) at night, including Witr (the odd-numbered prayer).
Hadith Referenceصحيح ابن خزيمه / جماع أبواب صلاة التطوع بالليل / 1167