Mukhtasar Bukhari (Abridged) 603 — Prophet's night prayer, sleep

Sayyiduna Anas (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) would sometimes refrain from fasting in a month to such an extent that we would think he would not fast at all in that month. But when he began to fast in a month, he would fast continuously until we thought he would not leave any day without fasting in that month. And regarding his (praying and sleeping), his condition was such that if you wished to see him praying at night, you could see him, and if you wished to see him sleeping, you could see him.