It is narrated from Sayyiduna Abu Ayyub (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Witr is a truth; whoever wishes may pray five rak'ahs, whoever wishes may pray three rak'ahs, and whoever wishes may pray one rak'ah; and whoever is overcome (by an excuse), let him pray it by gestures."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3952