Negative commandment · Lo Ta’aseh #361 of 613
Not to castrate one of all of the species
שלא לסרס זכר מכל המינין, לא אדם ולא בהמה חיה ועוף
The verse · Vayikra 22:24
וּמָעוּךְ וְכָתוּת וְנָתוּק וְכָרוּת לֹא תַקְרִיבוּ לַה׳ וּבְאַרְצְכֶם לֹא תַעֲשׂוּ
“You shall not offer to the Lord that which has its testicles bruised or crushed, or broken, or cut; neither shall you do thus in your land.”
The Rambam’s words
Not to castrate a male from any species - neither a human, a domestic animal, a wild beast, nor a bird, as [Leviticus 22:24] states: "You shall not do this in your land."
שלא לסרס זכר מכל המינין, לא אדם ולא בהמה חיה ועוף, שנאמר "ובארצכם, לא תעשו" (ויקרא כב,כד).
Why · Sefer HaChinuch #291
Not to castrate one of all of the species
“It is from the roots of the commandment [that it is] since G-d, blessed be He, created His world with absolute perfection — He did not miss nor add a thing in it from all that is fitting to be for its perfection.”
Who & when
“And this commandment is practiced in every place and at all times by males and females.”
Where in the Mishneh Torah
Hilchot Forbidden Intercourse הלכות איסורי ביאה