Sunan Ibn Majah, Chapter: The Chapters of Establishing the Prayer and the Sunnah Regarding Them

"I heard the Messenger of Allah (saw) say: 'Five prayers that Allah has enjoined upon His slaves, so whoever does them, and does not omit anything out of negligence, on the Day of Resurrection Allah will make a covenant with him that He will admit him to Paradise. But whoever does them but omits something from them out of negligence, will not have such a covenant with Allah; if He wills He will punish him, and if He wills, He will forgive him.'"