Sforno on Exodus 2:15/ספורנו על שמות ב׳:ט״ו

1. וישב בארץ מדין. He had decided to remain for a while in that country.

2וישב על הבאר. While Moses was traveling through the land of Midian it happened once that he settled near a certain (well known) well. The construction here is similar to Genesis 28,11) which describes Yaakov as encountering a certain place, also described with the preposition ה i.e. המקום instead of simply מקום, to show that the site had been known already.