Tawoos says that a man asked Sayyiduna Ibn Umar (may Allah be pleased with them) that Sayyiduna Abu Hurairah (may Allah be pleased with him) thinks that Witr is not obligatory? He replied: "Once a person asked the Prophet Muhammad (peace and blessings be upon him) about the night prayer. The Prophet (peace and blessings be upon him) said: 'You should pray two rak'ahs at a time, and when you fear that morning is near, then add one rak'ah to those two.'"
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 6258