Negative commandment · Lo Ta’aseh #258 of 613
Not to sell [a Hebrew servant] as slaves are sold
שלא למכור אותו ממכרת עבד
The verse · Vayikra 25:42
כִּי־עֲבָדַי הֵם אֲשֶׁר־הוֹצֵאתִי אֹתָם מֵאֶרֶץ מִצְרָיִם לֹא יִמָּכְרוּ מִמְכֶּרֶת עָבֶד
“For they are my servants, whom I brought out of the land of Miżrayim: they shall not be sold as bondmen.”
The Rambam’s words
Not to sell [a Hebrew servant] as slaves are sold, as [Leviticus 25:42] states: "Do not sell him as slaves are sold."
שלא למכור אותו ממכרת עבד, שנאמר "לֹא יִמָּכְרוּ מִמְכֶּרֶת עָבֶד" (ויקרא כה, מב).
Why · Sefer HaChinuch #345
That we not sell a Hebrew slave upon the auctioning stone
“The root of this commandment is well-known — that it is not fitting for a person to treat the honor of his fellow lightly; even if his sins have brought him to be sold.”
Who & when
“And [it] is practiced by males and females at the time that the Jubilee is practiced, as [the law of] Hebrew slaves is only practiced at the time of the Jubilee, as I wrote above (Sefer HaChinukh 330).”
Where in the Mishneh Torah
Hilchot Slaves הלכות עבדים