Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 58
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 58, with English translation by Maimonides (Rambam).
לאכול את בשר פסח שני על מצה ומרור, שנאמר: "עַל מַצּוֹת וּמְרוֹרִים יֹאכְלוּהוּ" (במדבר ט, יא).
To eat the meat of the second Paschal offering together with matzot and bitter herbs, as [Numbers 9:11] states: "And you shall eat it with matzot and bitter herbs."