Abu Dawud Book 2, Hadith Number 1364.

Chapter : The commandment of observing moderation in praying.

Narated By ‘Aisha : The Prophet (PBUH) called ‘Uthman b. Maz’un. When he came to him, he said: ‘Uthman, did you dislike my practice? He said: No, by Allah, but I seek your practice. He said: I sleep, I pray, I fast, I (sometimes) leave fast, and I marry women. Fear Allah, ‘Uthman, your wife has a right on you, your guest has a right on you, your self has a right on you; you should keep fast and (sometimes) leave fast, and pray and sleep.