Negative commandment · Lo Ta’aseh #147 of 613
Not to eat the meat of sacrifices of a lesser order of holiness before the sprinkling of their blood
שלא לאכול בשר קודשים קלים קודם זריקת דמים
The verse · Devarim 12:17
לֹא־תוּכַל לֶאֱכֹל בִּשְׁעָרֶיךָ מַעְשַׂר דְּגָנְךָ וְתִירֹשְׁךָ וְיִצְהָרֶךָ וּבְכֹרֹת בְּקָרְךָ וְצֹאנֶךָ וְכׇל־נְדָרֶיךָ אֲשֶׁר תִּדֹּר וְנִדְבֹתֶיךָ וּתְרוּמַת יָדֶךָ
“Thou mayst not eat within thy gates the tithe of thy corn, or of thy wine, or of thy oil, or the firstlings of thy herds or of thy flock, or any of thy vows which thou vowest, or thy freewill offerings, or offering of thy hand:”
The Rambam’s words
Not to eat the meat of sacrifices of a lesser order of holiness before the sprinkling of their blood, as [Deuteronomy, ibid.] states: "You may not [eat]... the [animals] you have pledged [to bring as sacrifices]..." - i.e., you are not allowed to eat from the sacrifices you have pledged until their blood has been sprinkled.
שלא לאכול בשר קודשים קלים קודם זריקת דמים, שנאמר "לא תוכל . . . ונדבותיך" (דברים יב,יז); כלומר, לא תוכל לאכול נדבותיך עד שייזרק דמם.
Why · Sefer HaChinuch #448
To not eat lower-level consecrated foods (kodashim kalim) before the sprinkling of the bloods
“It is from the roots of this commandment [that it is] to place into our hearts that it is always fitting for us to have benefit to our souls precede benefit to our bodies with everything in the world.”
Who & when
“And this prohibition is practiced in every place and at all times by males and females; as even one who consecrated his animal as lower-level consecrated foods today, and transgressed and ate a kazayit from it afterwards, is liable for lashes.”
Where in the Mishneh Torah
Hilchot Sacrificial Procedure הלכות מעשה הקרבנות