Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 74
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 74, with English translation by Maimonides (Rambam).
להקריב הזב קרבן אחר שיטהר, שנאמר: "וכי יטהר הזב, מזובו" (ויקרא טו,יג).
For a zav to offer a sacrifice when he becomes purified [after his affliction], as [Leviticus 15:13] states: "When a zav will become pure...."