Negative commandment · Lo Ta’aseh #254 of 613
Not to turn over a slave that fled from his master
שלא להחזיר עבד שברח לארץ ישראל לאדוניו שבחוצה לארץ
The verse · Devarim 23:16
לֹא־תַסְגִּיר עֶבֶד אֶל־אֲדֹנָיו אֲשֶׁר־יִנָּצֵל אֵלֶיךָ מֵעִם אֲדֹנָיו
“Thou shalt not deliver to his master the servant who is escaped from his master to thee:”
The Rambam’s words
Not to return a slave who fled to Eretz Yisrael to his master [who lives] in the Diaspora, as [Deuteronomy 23:16] states: "Do not deliver a servant to his master."
שלא להחזיר עבד שברח לארץ ישראל לאדוניו שבחוצה לארץ, שנאמר "לֹא תַסְגִּיר עֶבֶד אֶל אֲדוֹנָיו" (דברים כג, טז).
Who & when
“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.”
Where in the Mishneh Torah
Hilchot Slaves הלכות עבדים