Abu Dawud Book 2, Hadith Number 425.

Chapter : Not known.

Narated By Abdullah ibn Sunabihi : AbuMuhammad fancies that witr prayer is essential. (Hearing this) Ubadah ibn as-Samit said: Abu Muhammad was wrong. I bear witness that I heard the Apostle of Allah (PBUH) say: Allah, the Exalted, has made five prayers obligatory. If anyone performs ablution for them well, offers them at their (right) time, and observes perfectly their bowing and submissiveness in them, it is the guarantee of Allah that He will pardon him; if anyone does not do so, there is no guarantee for him on the part of Allah; He may pardon him if He wills, and punish him if He wills.