From 《
论语·
宪问》: when asked
以德报怨何如 ('How about repaying hatred with kindness?'), Confucius answered
何以报德?以直报怨,以德报德 - 'Then what do you repay kindness with? Repay hatred with fairness, and kindness with kindness.' The idiom survived as a moral ideal, though Confucius himself preferred proportionate fairness.