Negative commandment · Lo Ta’aseh #109 of 613
Not to sell the tithe of cattle
שלא למכור מעשר בהמה
The verse · Vayikra 27:33
לֹא יְבַקֵּר בֵּין־טוֹב לָרַע וְלֹא יְמִירֶנּוּ וְאִם־הָמֵר יְמִירֶנּוּ וְהָיָה־הוּא וּתְמוּרָתוֹ יִהְיֶה־קֹּדֶשׁ לֹא יִגָּאֵל
“He shall not search whether it be good or bad, neither shall he change it: and if he change it at all, then both it and its substitute shall be holy; it shall not be redeemed.”
The Rambam’s words
Not to sell the tithe of cattle, as [Leviticus 27:33] states: "It shall not be redeemed."
שלא למכור מעשר בהמה, שנאמר "לא ייגאל" (ויקרא כז,לג).
Why · Sefer HaChinuch #361
To not sell the tithe of beasts, but rather that it be eaten in Jerusalem
“It is from the roots of the commandment [that it is because] G-d chose the nation of Israel and wished for the sake of His righteousness that all of them be engaged with His Torah and be knowers of His Name.”
Who & when
“And this prohibition is practiced by males and females — Israelites, priests and Levites — in every place and at all times.”
Where in the Mishneh Torah
Hilchot Firstlings הלכות בכורות