Rashi on Exodus 2:21/רש"י על שמות ב׳:כ״א

1ויואל — Translate this as the Targum does: AND HE WAS WILLING. Similar are: (Judges 19:6) “Be content (הואל), I pray thee, and tarry all night”; (Joshua 7:7) “would that we had been content (הואלנו)”; (Genesis 18:31) “I am content (הואלתי) to speak”. A Midrashic explanation is that it has the sense of taking an oath (אלה), so that it should be rendered, “And Moses pledged himself by an oath to remain with the man” — he swore to him that he would not stir from Midian save by his permission (cf. Exodus 4:18) (Nedarim 65a).