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
← Previous Hadith 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 Next Hadith → I asked Anas about the fasting of the Prophet. He said "Whenever I liked to see the Prophet (ﷺ) fasting in any month, I could see that, and whenever I liked to see him not fasting, I could see that too, and if I liked to see him praying in any night, I could see that, and if I liked to see him sleeping, I could see that, too." Anas further said, "I never touched silk or velvet softer than the hand of Allah's Messenger (ﷺ) and never smelled musk or perfumed smoke more pleasant than the smell of Allah's Messenger (ﷺ)."

Sahih al-Bukhari Book 30, Hadith 80