heart of stone

From Ezekiel 36:25 of the King James Bible.

heart of stone (plural hearts of stone)

(figuratively, idiomatic) A hardhearted character, stern or cruel nature.
She's got a heart of stone.
- 2023 September 12, Phil McNulty, “Scotland 1-3 England: 'Complete package' Jude Bellingham puts concluding flourish on world-class performance”, in BBC Sport‎:
  It would take a heart of stone, or an opposition supporter, not to feel some measure of sympathy for a player whose career has come to a standstill at club level and does not seem able to catch a break when he does make a rare appearance.

stonehearted character

English