Abdullah bin Abbas (may Allah be pleased with them both) narrates from the Prophet (peace and blessings be upon him): "Three things are obligatory for me and voluntary for you: the sacrifice, witr, and the two rak'ahs of Duha (forenoon)."
Abu Janab al-Kalbi, whose name is Yahya bin Abi Hayyah, is da'if (weak); Yazid bin Harun used to regard him as truthful but accused him of tadlis (concealing the chain).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4459