Negative commandment · Lo Ta’aseh #106 of 613
Not to substitute [another animal] for [one selected as] a sacred offering
שלא להמיר את הקודשים
The verse · Vayikra 27:10
לֹא יַחֲלִיפֶנּוּ וְלֹא־יָמִיר אֹתוֹ טוֹב בְּרָע אוֹ־רַע בְּטוֹב וְאִם־הָמֵר יָמִיר בְּהֵמָה בִּבְהֵמָה וְהָיָה־הוּא וּתְמוּרָתוֹ יִהְיֶה־קֹּדֶשׁ
“He shall not alter it, nor change it, a good for a bad, or a bad for a good: and if he shall at all change beast for beast, then it and its substitute shall be holy.”
The Rambam’s words
Not to substitute [another animal] for [one selected as] a sacred offering, as [Leviticus 27:10] states: "Do not exchange it or substitute another for it."
שלא להמיר את הקודשים, שנאמר "לא יחליפנו, ולא ימיר אותו" (ויקרא כז,י).
Why · Sefer HaChinuch #351
To not exchange consecrated things
“The root of this commandment and some of its laws are all written in this Order in the next commandment.”
Who & when
“And this prohibition is practiced in every place and at all times by males and females.”
Where in the Mishneh Torah
Hilchot Substitution הלכות תמורה