Sayyiduna Abu Hurayrah (may Allah be pleased with him) said: My close friend (peace and blessings be upon him) advised me of three things: "Praying witr before sleeping, fasting three days of every month, and the two rak'ahs of Duha (forenoon)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4897