It's when the jews said that jibreel 'alayhis salaam is their enemy because he comes to destroy the sinners etc, and then Allaah revealed aayah 97 of surah baqarah, qul man kaana 'aduwwal li jibreel fa'innahu nazzalahu 'alaa qalbika bi idhnillaahi musaddiqal limaa bayna yadayhi wa hudaw wa bushraa lil mu'mineen.