Positive commandment · Mitzvat Aseh #86 of 613
To redeem consecrated things upon which a blemish developed
לפדות קודשים בעלי מומים ויהיו מותרים באכילה
The verse · Devarim 12:15
רַק בְּכׇל־אַוַּת נַפְשְׁךָ תִּזְבַּח וְאָכַלְתָּ בָשָׂר כְּבִרְכַּת ה׳ אֱלֹהֶיךָ אֲשֶׁר נָתַן־לְךָ בְּכׇל־שְׁעָרֶיךָ הַטָּמֵא וְהַטָּהוֹר יֹאכְלֶנּוּ כַּצְּבִי וְכָאַיָּל
“Nonetheless, thou mayst slaughter animals and eat their flesh to thy heart’s desire, according to the blessing of the Lord thy God which he has bestowed on thee, throughout all thy gates, the unclean and the clean may eat of it as they do of the gazelle and the deer.”
The Rambam’s words
To redeem sacred offerings that have become blemished, and thus have them to be permitted [for mundane use], as [Deuteronomy 12:15] states: "But whenever you desire, you may slaughter...." Based on the oral tradition, we have learned that this refers only to sacred offerings which have become disqualified and have been redeemed.
לפדות קודשים בעלי מומים ויהיו מותרים באכילה, שנאמר: "רק בכל אוות נפשך תזבח ואכלת בשר" (דברים יב,טו); מפי השמועה למדו שאינו מדבר אלא בפסולי המוקדשין שייפדו.
Why · Sefer HaChinuch #441
To redeem consecrated things upon which a blemish developed
“It is from the roots of the commandment that it was from the kindnesses of G-d to us to permit us to derive benefit from the sacrificial animals after they develop a blemish — and even though they were already separated to be consecrated and the power of the name of the Heavens rested upon them.”
Who & when
“And this commandment is practiced by males and females at the time of the [Temple].”
Where in the Mishneh Torah
Hilchot Things Forbidden on the Altar הלכות איסורי המזבח