condemn the offense, but not the offender
Proverb advising to separate the wrong act from the person who committed it; hate the sin, not the sinner.
See also: その罪を憎んでその人を憎まず
As the saying goes, 'condemn the offense, but not the offender'; even if you can't forgive what he did, you shouldn't hate him as a person.
Based on a maxim in the Chinese 『孔叢子』, presented there as a saying of Confucius: condemn the wrongful intention or deed without hating the person.