Midrasch zu Divrej Hajamim I 17:27

(Devarim 1:5) "Across the Jordan, in the land of Moav, Moses ho'il (began) to explain": "hoalah" is "beginning," as in (Judges 19:6) "Begin ("hoel") now and stay overnight so that you will be refreshed," and (I Chronicles 17:27) "and now you have begun ("hoalta") to bless the house of your servant to be before You forever." And the sages say: "hoalah" is "swearing," as in (Shemoth 2:21) "And Moses swore ("vayoel") to remain with the man," and (I Samuel 14:24) "And Saul beswore ("vayoel") the people, saying 'Cursed be the man who will eat bread until the evening when I will be avenged of my enemies.'"