Sahih Muslim 2059
Sahih Muslim · Book 36: The Book of Drinks · The virtue of sharing a small amount of food, and the food of two is sufficient for three, and so on.
Jabir reported Allah's Messenger (ﷺ) as saying:
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ ، وَعُثْمَانُ بْنُ أَبِي شَيْبَةَ ، قَالاَ حَدَّثَنَا جَرِيرٌ ، عَنِ الأَعْمَشِ ، عَنْ أَبِي سُفْيَانَ ، عَنْ جَابِرٍ ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " طَعَامُ الرَّجُلِ يَكْفِي رَجُلَيْنِ وَطَعَامُ رَجُلَيْنِ يَكْفِي أَرْبَعَةً وَطَعَامُ أَرْبَعَةٍ يَكْفِي ثَمَانِيَةً " .
Food for one (person) suffices two, and food for two (persons) suffices four persons and food for four persons suffices eight persons.