The Prophet (ﷺ) never fasted a full month except the month of Ramadan, and he used to fast till one could say, "By Allah, he will never stop fasting," and he would abandon fasting till one would say, "By Allah, he will never fast."
Sahih al-Bukhari Book 30, Hadith 78
← Previous Hadith The Prophet (ﷺ) never fasted in any month more than in the month of Sha'ban. He used to say, "Do those deeds which you can do easily, as Allah will not get tired (of giving rewards) till you get bored and tired (of performing religious deeds)." The most beloved prayer to the Prophet (ﷺ) was the one that was done regularly (throughout the life) even if it were little. And whenever the Prophet (ﷺ) offered a prayer he used to offer it regularly .

Sahih al-Bukhari Book 30, Hadith 77 Next Hadith → Allah's Messenger (ﷺ) used to leave fasting in a certain month till we thought that he would not fast in that month, and he used to fast in another month till we thought he would not stop fasting at all in that month. And if one wanted to see him praying at night, one could see him (in that condition), and if one wanted to see him sleeping at night, one could see him (in that condition) too.

Sahih al-Bukhari Book 30, Hadith 79