Praise be to Allah.The majority of scholars (jumhoor ul-'ulmeaa') assert that salaat ul-witr (witr prayer) is a sunnah mu'akkada (confirmed sunnah that the Prophet peace be upon him, practiced consistently), and that it is not obligatory. This is based on the hadith (saying) regarding the bedouin who once came to the Prophet asking about Islam, the Prophet answered, "Five prayers within one day-and-night." The bedouin asked, "Am I obliged to other than those?" The Prophet replied, "Unless you volunteer of your own." (al-hadith muttafaqun alaih.)
Some scholars have said that qiyaam ul-layl (prayer at the heart of night) and salaat ul-witr are the best of the voluntary prayers (al-nawaafil). Therefore, one should consistently practice them and not neglect them. The Prophet did not neglect the prayers during night nor two rak'ah before al-fajr neither in residence nor in travel (as related in al-sunnah al-sahihah).