In Claudius' soliloquy in Act 3, Scene 3, lines 73-87, his struggle to pray for forgiveness.

In the soliloquy, Claudius looks into his soul and is deeply disgusted by what he sees. He kneels to pray, hoping to purge his guilt, but reflects that this penance will not be genuine because he will still retain the prizes for which he committed murder in the first place, his crown and his wife.