Hachnasas Orchim and the Reward of Gan Eden

It states (21:33) ,אשל ויטע and ל"אש is roshei teivos for לוויה שתיה אכילה, referring to Avraham's hachnasas orchim for tired and hungry travelers who benefited immensely from Avraham's kind service. However, the elaboration of Avraham's hospitable deeds is explicitly written at the beginning of the parashah, when he served the three malachim who didn’t need to eat or drink!

Reb Shlomo Zalman Auerbach zt'l explains that the Torah wanted to elaborate on how Avraham’s hachnasas orchim when he was weak, on the third day after his milah, because a mitzvah is measured according to how hard it is to perform.

Other time is in Bereishis (2:8) בעדן גן אלקים 'ה ויטע. This teaches us that those who engage in hachnasas orchim will merit Gan Eden.