Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 189
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 189, with English translation by Maimonides (Rambam).
שלא לאכול פת תבואה חדשה קודם הפסח, שנאמר "ולחם . . . לא תאכלו" (ויקרא כג,יד).
Not to eat bread made from newly grown produce before Pesach, as [Leviticus 23:14] states: "[Until that day,...] you may not eat bread..."