Know that the fast of Ramadan was made obligatory in the second year after the hijra to al Madinah, on Monday the second of Sha’bān. As such, the Prophet صلى الله عليه وسلم fasted nine Ramadans.
Eight of them were 29 days and one was a complete 30 days based on the most reliable statement. Other statements have been narrated
as Sheikh Muhammad_Ādam_al Ithiōpī
Source:# The Explanation of Sahīh_Muslim pg.362, v.20