Positive commandment · Mitzvat Aseh #118 of 613
Addition of a fifth for one who eats from the consecrated or misappropriates it
לשלם השוגג במעילה מה שמעל לה' ולהוסיף חומש
The verse · Vayikra 5:16
וְאֵת אֲשֶׁר חָטָא מִן־הַקֹּדֶשׁ יְשַׁלֵּם וְאֶת־חֲמִישִׁתוֹ יוֹסֵף עָלָיו וְנָתַן אֹתוֹ לַכֹּהֵן וְהַכֹּהֵן יְכַפֵּר עָלָיו בְּאֵיל הָאָשָׁם וְנִסְלַח לוֹ
“And he shall make amends for the wrong that he has done in the holy thing, and shall add the fifth part to it, and give it to the priest: and the priest shall make atonement for him with the ram of the guilt offering, and it shall be forgiven him.”
The Rambam’s words
For a person who unintentionally makes use of a sacred object to make restitution for what he misused [when] sinning against G-d, and for him to add one fifth of its value, as [Leviticus 5:17] states: "For that which he sinned, [using something] sacred, he shall pay...."
לשלם השוגג במעילה מה שמעל לה' ולהוסיף חומש, שנאמר: "וְאֵת אֲשֶׁר חָטָא מִן הַקֹּדֶשׁ יְשַׁלֵּם" (ויקרא ה, טז).
Why · Sefer HaChinuch #127
Addition of a fifth for one who eats from the consecrated or misappropriates it
“From the roots of the commandment are what you will see at the end of my words. However, I am afraid of drawing close to the Dwelling of G-d, as I know that “anyone who comes close, who comes close” that has not sufficiently sanctified himself “will not see the House and live.””
Who & when
“And [it] is practiced at the time of the [Temple] by males and females.”
Where in the Mishneh Torah
Hilchot Trespass הלכות מעילה