Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 215
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 215, with English translation by Maimonides (Rambam).
שלא לזרוע כלאי זרעים, שנאמר "שדך לא תזרע כלאיים" (ויקרא יט,יט).
Not to sow mixed species of seeds together, as [Leviticus 19:19] states: "Do not sow different species of seed in your field."