Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 64
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 64, with English translation by Maimonides (Rambam).
מעשה חטאת, שנאמר: "זֹאת תּוֹרַת הַחַטָּאת" (ויקרא ו, יח).
The sin offering, as [Leviticus 6:18] states: "These are the laws of the sin offering...."