Sahih Muslim 2058
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.
Abu Huraira reported Allah's Messenger (ﷺ) as saying:
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى ، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ أَبِي الزِّنَادِ ، عَنِ الأَعْرَجِ ، عَنْ أَبِي هُرَيْرَةَ ، أَنَّهُ قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " طَعَامُ الاِثْنَيْنِ كَافِي الثَّلاَثَةِ وَطَعَامُ الثَّلاَثَةِ كَافِي الأَرْبَعَةِ " .
Food for two persons suffices three persons and food for three persons suffices four persons.