Sefer HaChinuch ספר החינוך

That we not sell a Hebrew slave upon the auctioning stone: That we not sell a Hebrew slave in the way that we sell Canaanite (gentile) slaves, by announcement upon the auctioning stone, but rather discreetly and in an honorable fashion. And so did they say (Sifra, Behar, Section 6:1), “‘They shall not be sold with the sale of a slave’ (Leviticus 25:42) — that they not be sold in a market-stand and be placed up on 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. As he does not know if maybe tomorrow, he will also come to this. The elucidation of this commandment is in Kiddushin and its laws are included in its essence — there is no need to be lengthy about them.

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). And one who transgresses this and sells a Hebrew slave in the way that Canaanite slaves are sold has violated a negative commandment. But from what appears, there is no liability for lashes, since it is possible to transgress it without an act.