Musnad Ahmad 2:122

Hashim ibn al-Qasim narrated to us, 'Ikrimah—meaning ibn 'Ammar—narrated to us, Simak al-Hanafi Abu Zumayl narrated to me, he said: 'Abdullah ibn 'Abbas narrated to me. 'Umar ibn al-Khattab narrated to me, he said: When the day of Khaybar arrived, a group of the companions of the Prophet, may Allah bless him and grant him peace, came forward and said: "So-and-so is a martyr, so-and-so is a martyr," until they passed by a man and said: "So-and-so is a martyr." The Messenger of Allah, may Allah bless him and grant him peace, said: "Nay, I have seen him in the Fire in a garment he misappropriated, or a cloak." Then the Messenger of Allah, may Allah bless him and grant him peace, said: "O son of al-Khattab, go and call out among the people: 'Indeed, none shall enter Paradise except the believers.'" He said: So I went out and called out: "Indeed, none shall enter Paradise except the believers."