Sahih Bukhari
Food, Meals
Volume: 007 / Book Number: 065 / Hadith Number: 309
Narrated Abu Huraira:
A man used to eat much, but when he embraced Islam, he started eating less. That was mentioned to the Prophet who then said, "A believer eats in one intestine (is satisfied with a little food) and a Kafir eats in seven intestines (eats much). "