Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 279
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 279, with English translation by Maimonides (Rambam).
שלא לרחם על המזיק בדיני קנסות, שנאמר "לֹא תָחוֹס עֵינְךָ" (דברים יט, כא).
Not to have pity on a person who has caused damages in judgments concerning fines, as [Deuteronomy 25:12] states: "Let your eye not pity."