Sefer HaChinuch ספר החינוך

Not to turn over a slave that fled from his master: That we have been prevented from returning a slave that fled from his master outside of the Land, [who came] to the Land of Israel. (See Sefer HaMitzvot, Negative Commandments 254.) And even if his master is an Israelite, we do not return [the slave] to him. But [rather], we free him and write down his value as a debt on himself. And about this is it stated, (Deuteronomy 23:16), “You shall not turn over a slave to his master.” And so is it elucidated in Tractate Gittin 45a, that the verse is speaking about a slave that fled from outside of the Land to the Land of Israel. And they said there that the law about him is that we write a contract with his value [as a debt] for him and we [also] write a contract of [his] freedom; and that we not return him to slavery in any way — since he entered the chosen valley of purity to serve God, may He be blessed, there.

That which we mentioned is from the roots of this commandment — that God wanted for the honor of the Land, that one who flees to there be saved from slavery; in order that we place the honor of the place into our hearts and fix the awe of God, may He be elevated, into our hearts, when we are there. And all of this is to help His people and to give them merit, as He is one Who desires kindness.

The laws of the commandment are elucidated there in Tractate Gittin.

And this commandment is practiced even in our day by males and females, as all are warned not to return him to his master, since he has fled to the Chosen Land. And one who transgresses this and seizes him and returns him to his master, has violated this negative commandment. But according to what appears, there is no obligation for [getting] lashes, since the obligation is only when he returns him to slavery; and maybe his master will no longer enslave him — and we do not give lashes, [in the case] of a doubt.