It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that once a man came to the service of the Prophet (peace and blessings be upon him) and inquired about the night prayer. The Prophet (peace and blessings be upon him) said: "The night prayer consists of two rak'ahs at a time, and when you fear that dawn is approaching, then add one rak'ah to these two, and that will suffice as witr for all the prayers you have offered during the night."