Muslim

Ibn Abbas (RA) (Allah be pleased with both of them) reported: The Messenger of Allah (ﷺ) did not fast throughout any month except during Ramadan. And when he observed fast (he fasted so continuously) that one would say that he would not break (them) and when he abandoned, he abandoned (so continuously) that one would say: By Allah, perhaps he would never fast.

This hadith has been narrated on the authority of Abu Bishar with the same chain of transmitters (with a slight variation of words and these are), that he (the narrator) said: "During any month continuously since he came to Madinah."

'Uthman bin Hakim al-Ansari said: I asked Sa'id bin Jubair 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 continuously) that we (were inclined to say) that he would not observe fast.

The same hadith as the previous hadith has been transmitted through another chain.