Uthman b. Hakim al-Ansari Radi allahu anhu said I asked Sa'id b

✦ Uthman b. Hakim al-Ansari Radi allahu anhu said I asked Sa'id b. Jubair radi allahu amhu about fasting In Rajab, and we were then passing through the month of Rajab, whereupon he said: I heard Ibn 'Abbas (Allah be pleased with both of them) as saying: The Messenger of Allah (ﷺ) used to observe fast (so continuously) that we (were inclined) to say that he would not break (them) and did not observe them so conti- nuously) that we (were inclined to say) that he would not observe fast. - 

Sahih Muslim, Book 6, 2585

✦ It was narrated that Abu Dharr said: My beloved Prophet advised me to do three things which I will never give up, if Allah wills. He advised me to pray Duha, to pray Witr before sleeping, and to fast three days of each month."

Sunan Nasaii, Book 22, 2406-Sahih