Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 302
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 302, with English translation by Maimonides (Rambam).
שלא לשנוא בלב, שנאמר "לֹא תִשְׂנָא אֶת אָחִיךָ בִּלְבָבֶךָ" (ויקרא יט, יז).
Not to bear hatred in one's heart, as [Leviticus 19:17] states: "Do not hate your brother in your heart."