Rashi on Genesis 19:22/רש"י על בראשית י״ט:כ״ב

1כי לא אוכל לעשות FOR I CANNOT DO [ANY THING]—This admission of their powerlessness was the angels’ punishment for having said, (v. 13) “For we will destroy the city”, attributing the act to themselves; therefore they could not go away from there (i. e., the incident could not close) until they were compelled to admit that the thing was not in their power) (Genesis Rabbah 50:9).

2כי לא אוכל FOR I CANNOT DO ANY THING — The pronoun is singular number. This proves that one was to overthrow the city and the other to deliver, for two angels are not sent on the same mission.

3על כן קרא שם העיר צוער THEREFORE THE NAME OF THE CITY WAS CALLED ZOAR, with reference to Lot’s words (v. 20) “And it is (מצער) a little one”.