A guest came to the Messenger of Allah ﷺ while he was still a disbeliever, so the Messenger of Allah ﷺ ordered that a sheep be milked, and the disbeliever drank its milk. Then another was milked, and he drank it. Then another, and he drank that too, until he had drunk the milk of seven sheep.The next morning he embraced Islam, so the Messenger of Allah ﷺ ordered a sheep to be milked for him, and he drank its milk. Then another was ordered, but he could not finish it.The Messenger of Allah ﷺ said, "The believer eats with one stomach, and the disbeliever eats with seven stomachs."
حدثنا إسحاق أنبأنا مالك عن سهيل عن أبيه
أن رسول الله ﷺ ضافه ضيف وهو كافر فأمر رسول الله ﷺ بشاة فحلبت فشرب الكافر حلابها ثم أخرى فشربه ثم أخرى فشربه حتى شرب حلاب سبع شياه ثم إنه أصبح فأسلم فأمر له رسول الله ﷺ بشاة فشرب حلابها ثم أمر بأخرى فلم يستتمها فقال رسول الله ﷺ المؤمن يأكل في معى واحد والكافر يأكل في سبعة أمعاء
Its isnad is sahih, it was mentioned frequently before, see number 4718. It was also reported by Bukhari 7/92 in the Book of Foods, chapter "The believer eats with one stomach," Muslim 3/1631 number 2061 in the Book of Drinks, chapter "The believer eats with one stomach," Tirmidhi 4/267 number 1818 in the Book of Foods, chapter "The believer eats with one stomach," Ibn Majah 2/1084 number 3256 in the Book of Foods, chapter "The believer eats with one stomach," Darimi 2/99, and Ibn Abu Shayba 8/133.