Narrated Abu Ayyub al-Ansari (RA): The Prophet (peace be upon him) said: The witr is a duty for every Muslim so if anyone wishes to observe it with five rak’ahs, he may do so; if anyone wishes to observe it with three, he may do so, and if anyone wishes to observe it with one, he may do so.
Sunan Abi Dawud, Book 8, Hadith 7
