Sahih Al Bukhari – Book of Food, Meals

Volumn 007, Book 065, Hadith Number 305.
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Narated By Nafi' : Ibn 'Umar never used to take his meal unless a poor man was called to eat with him. One day I brought a poor man to eat with him, the man ate too much, whereupon Ibn 'Umar said, "O Nafi'! Don't let this man enter my house, for I heard the Prophet saying, "A believer eats in one intestine (is satisfied with a little food), and a kafir (unbeliever) eats in seven intestines (eats much food)."