Musnad Ahmad 1018:4

Ibn Numayr narrated to us, from Uthman—meaning Ibn Hakim—Tamim ibn Yazid, the freed slave of Banu Zam'ah, informed me, from a man among the companions of the Messenger of Allah (peace and blessings of Allah be upon him), who said: The Messenger of Allah (peace and blessings of Allah be upon him) addressed us one day, then said: "O people, two things—whoever Allah protects from their evil shall enter Paradise." He said: A man from the Ansar stood up and said: "O Messenger of Allah, will you not tell us what they are?" Then he said: "Two things—whoever Allah protects from their evil shall enter Paradise." Until, when it was the third time, the companions of the Messenger of Allah (peace and blessings of Allah be upon him) made him sit down and said: "Do you see the Messenger of Allah wishing to give us glad tidings, and you prevent him?" He said: "I fear that people will rely [upon that]." Then he said: "Two things—whoever Allah protects from their evil shall enter Paradise: what is between his two jaws, and what is between his two legs."