The Ruling on the Hadith: We Are a People Who Do Not Eat Until We Are Hungry

Q: Regarding this hadith, we do not know its authenticity. It is: (We are a people who do not eat until we are hungry, and when we eat, we do not become full).

A: This is narrated from some of the delegations, and there is weakness in its chain of narration. It is narrated that they said to the Prophet (peace and blessings be upon him): (We are a people who do not eat until we are hungry, and when we eat, we do not become full), meaning that they are moderate. This meaning is correct, but the chain of narration is weak. [Refer to Zad al-Ma'ad, and al-Bidaya wa al-Nihaya by Ibn Kathir].
This benefits a person if he eats when he is hungry or in need, and if he does not overeat when he eats, and does not fill himself with excessive fullness. As for fullness that does not cause harm, there is nothing wrong with it.
So people used to eat and become full in the time of the Prophet (peace and blessings be upon him) and in other times, but there is fear of apparent, excessive fullness. The Prophet (peace and blessings be upon him) was sometimes invited to feasts, and he would host people and order them to eat, so they would eat and become full. Then he would eat afterwards, (may Allah's prayers and peace be upon him), along with the remaining Companions.
In his time, it is narrated that Jabir ibn Abdullah al-Ansari invited the Prophet (peace and blessings be upon him) on the Day of the Confederates, the Day of the Battle of the Trench, to food consisting of a small slaughtered animal—a kid goat—and some barley. The Prophet (peace and blessings be upon him) ordered the bread and meat to be cut, and he would call for ten people at a time, so they would eat and become full, then they would go out and another ten would come, and so on. So Allah blessed the barley and the kid goat, and a large group ate from it, and a great remainder was left until they distributed it to the neighbors.
The Prophet (peace and blessings be upon him) also gave the people of the Safa milk to drink on one day. Abu Hurayrah said: So I gave them to drink until they were satisfied. Then the Prophet (peace and blessings be upon him) said: I drank. Then he said: So I drank. Then he said: So I drank. Then I said, by Him who sent you with the truth, I do not find a path for it. Then the Prophet (peace and blessings be upon him) took what remained and drank, (may Allah's prayers and peace be upon him). This indicates the permissibility of fullness and the permissibility of quenching thirst, but without harm.