Abud-Darda (May Allah be pleased with him) reported:
My friend (the Messenger of Allah) (ﷺ) directed me to observe Saum (fasting) for three days in every month, to perform two Rak'ah (optional) Duha prayer at forenoon, and to perform the Witr prayer before going to bed.[Al-Bukhari and Muslim].
App reference: Book 9, Hadith 269
Arabic/English book reference: Book 9, Hadith 1259