וְלֹ֥א תָח֖וֹס עֵינֶ֑ךָ נֶ֣פֶשׁ בְּנֶ֗פֶשׁ עַ֤יִן בְּעַ֙יִן֙ שֵׁ֣ן בְּשֵׁ֔ן יָ֥ד בְּיָ֖ד רֶ֥גֶל בְּרָֽגֶל׃ (ס)
And thine eye shall not pity: life for life, eye for eye, tooth for tooth, hand for hand, foot for foot.
Sefer HaChinukh
To not show pity upon the killer or injurer: That we were prevented from having mercy upon the one that killed his fellow or removed one of his limbs; that the judge not say, "This poor man that cut off the hand of his fellow or blinded his eye, he did not do it intentionally," and he have mercy upon him from having him repay [the injured] according to his evil. And about this is it stated (Deuteronomy 19:21), "And your eye shall not show mercy, a soul for a soul, etc." And the prevention of this is repeated in a different place, as it is stated (Deuteronomy 19:13), "Your eye shall not show mercy upon him, and you shall purge the innocent blood."