Volume 2, Book 21, Number 242:
Narrated Anas bin Malik:
Sometimes Allah’s Apostle would not fast (for so many days) that we thought that he would not
fast that month and he sometimes used to fast (for so many days) that we thought he would not leave
fasting through-out that month and (as regards his prayer and sleep at night), if you wanted to see
him praying at night, you could see him praying and if you wanted to see him sleeping, you could
see him sleeping.