Negative commandment · Lo Ta’aseh #219 of 613
To not muzzle an animal at the time of its work
שלא לחסום בהמה בשעת מלאכה בדבר שאוכלת ממנו ונהנית
The verse · Devarim 25:4
לֹא־תַחְסֹם שׁוֹר בְּדִישׁוֹ
“Thou shalt not muzzle the ox when he treads out the corn.”
The Rambam’s words
Not to muzzle an ox while it is working with produce from which it would eat and derive benefit, as [Deuteronomy 25:4] states: "Do not muzzle an ox while it is treading grain."
שלא לחסום בהמה בשעת מלאכה בדבר שאוכלת ממנו ונהנית, שנאמר "לא תחסום שור, בדישו" (דברים כה,ד).
Why · Sefer HaChinuch #596
To not muzzle an animal at the time of its work
“It is from the roots of the commandment [that it is] to teach ourselves that our souls be a good soul that chooses what is right and clings to it and pursues kindness and mercy.”
Who & when
“And this prohibition is practiced in every place and at all times by males and females.”
Where in the Mishneh Torah
Hilchot Hiring הלכות שכירות