Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.081.

The number of prayers prescribed by Allah is five. Ibn Mahyraiz narrated that al-Makhdaji, from the tribe of Kananah, heard Abu Muhammad–a man in ash-Shams–saying, “The witr prayer is obligatory.” He said he went to ‘Ubadah ibn as-Samit and informed him of this. ‘Ubadah corrected him, saying, “Abu Muhammad is mistaken. I heard the Messenger of Allah, upon whom be peace, say ‘Allah has laid five prayers upon His slaves. Whoever fulfils them and does not miss any of them will have a pact with Allah that He will let him enter Paradise. Whoever does not come with them will have no pact with Allah. If He wishes, He may punish him, and if He wishes, He may forgive him.” (Related by Ahmad, Abu Dawud, an-Nasa’i and Ibn Majah.) In one version it states, “Or one who comes with a deficiency in them or who degrades their duties.” Talhah ibn ‘Ubaidullah narrated that a bedouin with unkempt hair came to the Messenger of Allah, upon whom be peace, and said, “O Messenger of Allah, inform me of what Allah has made obligatory on me as regards praying.” He said, “Five prayers, unless you do others voluntarily.” He asked the Prophet to inform him about fasting, and he said, “The fast of Ramadan, unless you do others voluntarily.” Then he asked him about charity…and the Messenger of Allah informed him of the Islamic legislations. The bedouin then said, “By the One who has honoured you, I shall not voluntarily add anything to it, nor shall I be deficient in what Allah has ordered me to do.” The Messenger of Allah, upon whom be peace, then said, “He will enter Paradise if he is truthful (to what he said).” (Related by al-Bukhari and Muslim.)