"He perceived no iniquity in Yaakov" [Balak 23:21]
R' Levi Yitzchak of Berdichev remarked:
Hashem, to Whom everything is revealed and known, does not look at the sins of a Jew, as the verse states: "He does not look [lo hibit] at the iniquity in Yaakov".
If this is the way of Hashem, how much more so is it forbidden for us - flesh and blood - to look at the sins of another Jew! We, too, must cling to this lofty trait of "He does not look at the iniquity in Yaakov".
Source: Rabbi Yisrael Bronstein