I studied Latin in 7th grade, and my teacher used to read some stories from Greek and Roman mythology to us. There is one of those that I wanted to learn more about, but haven't been able to find. Here is what I remember. Bear with me, that was over twenty years ago.
One god (or two?) is travelling disguised as a mortal. He asks an elderly, poor couple for hospitality, and is very well received. The couple goes as far as killing its only goose to feed the traveller.
If I remember correctly, they keep serving wine to the traveller, and realise something is weird because the amphora remains full.
Eventually the traveller reveals that he is a god and, to thank them for their generosity, turns them both into a tree, half oak and half olive tree or something of the sort, so that they will remain forever together.
As I said, it was a very long time ago, and I may have some elements wrong, but I think I remember the general idea correctly. Does someone know what Greek and/or Roman myth this is?