Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 300
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 300, with English translation by Maimonides (Rambam).
שלא להוסיף במלקות המחוייב מלקות, שנאמר "לא יוסיף: .פן יוסיף" (דברים כה,ג).
Not to add lashes when whipping a person liable for such punishment, as [Deuteronomy 25:3] states: "Do not add [lashes], lest by [giving him] this additional [punishment]...."