Sunan An-Nasai, Chapter: The Book of Salah

that a man from Banu Kinanah who was called Al-Mukhdaji heard a man in Ash-Sham, who was known as Abu Muhammad (SAW), saying that Witr was obligatory. Al-Mukhdaji said: "In the morning I went to 'Ubadah bin As-Samit, and I met him while he was on his way to the Masjid. I told him what Abu Muhammad (SAW) said, and 'Ubadah said: 'Abu Muhammad (SAW) is wrong. I heard the Messenger of Allah (saw) say: 'Five prayers are those that Allah has decreed for (His) slaves, whoever does them, and does not neglect any of them out of disregard toward them, will have a promise from Allah that He will admit him to Paradise. And whoever does not do them will have no such promise from Allah; if He wills he will punish him and if He wills He will admit him to Paradise.'" (Hasan)