'There are three things regarding which Allah, the Exalted, did not allow any flexibility: returning a trust to its owner, be he good or wicked; keeping one's pact with both the good and the wicked; and kindness to one's parents whether they be good or wicked.'
Imam Muhammad ibn Ali al-Baqir [as]
al-Kafi, v. 2, p. 162, no. 15