Food for two persons suffices for three, and food for three persons suffices for four
Authentic hadithعن أبي هريرة رضي الله عنه قال: قال رسول الله صلى الله عليه وسلم : "طعام الاثنين كافي الثلاثة، وطعام الثلاثة كافي الأربعة". وفي رواية لمسلم عن جابر رضي الله عنه عن النبي صلى الله عليه وسلم قال: "طعام الواحد يكفي الاثنين، وطعام الاثنين يكفي الأربعة، وطعام الأربعة يكفي الثمانية".
Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "Food for two persons suffices for three, and food for three persons suffices for four." In Muslim's narration, Jābir (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "Food for one person suffices for two, and food for two persons suffices for four, and food for four persons suffices for eight."
Explanation
The Hadīth urges Muslims to share food. Even if it is a small amount, the desired sufficiency will still be attained, and blessing will fall upon it and thus showers all those sharing in it. It is also an encouragement from the Prophet, may peace and blessings be upon him, towards altruism. That is to say, if you have some food that, in your estimation, shall be enough for you only, and another person comes, do not be stingy and say this food is mine alone. Rather, give him some of it as it will suffice for two persons.
Source · Narrated by Muslim - Narrated by Bukhari & Muslim
From the Hadith Encyclopedia (hadeethenc.com).