heap coals of fire on one's head
heap coals of fire on one's head {v. phr.}, {literary}
To be kind or helpful to someone who has done wrong to you, so that he is ashamed.
Alice heaped coals of fire on Mary's head by inviting her to a party after Mary had gossiped about her.
Jean Valjean stole the Bishop's silver, but the Bishop heaped coals of fire on his head by giving the silver to him.
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Source: A Dictionary of American Idioms