Abdullah bin Tha'labah al-Udhri (may Allah be pleased with him), who was one of the Companions of the Prophet (peace and blessings be upon him) and whose face the Prophet had wiped, said: I saw Sa'd bin Abi Waqqas (may Allah be pleased with him): when he prayed Isha, he would pray one rak'ah of witr. In another narration from Yunus it adds: until he would rise in the depth of the night.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4786