Volume 3, Book 31, Number 193:
Narrated Anas:
Allah’s Apostle 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.