Ikrimah narrates from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Three things are obligatory upon me and voluntary for you: offering a sacrifice, praying the witr, and offering the two rak'ahs of the forenoon (duha) prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19030