Musnad Ahmad 30:972

Abu al-Yaman narrated to us, Shu'ayb informed us, from al-Zuhri, Ibn al-Musayyib informed me, that Abu Hurayrah said: We witnessed Khaybar with the Prophet, may God bless him and grant him peace. The Prophet, may God bless him and grant him peace, said to a man who was with him, who was claimed to be of Islam: "Indeed, this one is of the people of the Fire." He mentioned the meaning of it, except that he said: It became severe upon the men of the Muslims, so they said: "O Messenger of God, God has proven your speech true, for so-and-so has committed suicide and killed himself."