Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates: "My close friend (peace and blessings be upon him) advised me to do three things: to fast three days of every month, to offer the two rak'ahs of Duha, and to sleep after (praying) Witr."
(In the narration of Ibn Furak: praying Witr before sleeping, and he said: the Duha prayer.)
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8436