Musnad Ahmad 27:571

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Waqid ibn Muhammad ibn Zayd, that he heard Nafi' say: Ibn Umar saw a poor man, so he began to bring him closer and place [food] before him. He [the man] began to eat a great deal. He [Ibn Umar] said to me: "Do not let this man enter upon me, for I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: 'Indeed, the disbeliever eats in seven intestines.'"