Musnad Abu Ya'la al-Mawsili 243:44

Abu Kurayb narrated to us, Abu Usamah narrated to us, from Burayd, from Abu Burdah, from Abu Musa, from the Prophet (peace and blessings of Allah be upon him), who said: "The believer eats in one intestine, and the disbeliever eats in seven intestines."