לֹא־יַחֲבֹ֥ל רֵחַ֖יִם וָרָ֑כֶב כִּי־נֶ֖פֶשׁ ה֥וּא חֹבֵֽל׃ (ס)
人不可拿下磨或上磨石作抵押，因為這是拿人賴以活命的東西作抵押。
Rashi
לא יחבל NO MAN SHALL TAKE [THE LOWER OR THE UPPER MILLSTONE] AS PLEDGE — i.e. if one comes to demand a pledge through the court for his debt he should not take as a pledge anything by which food is prepared (Bava Metzia 113b, 115a).
Ibn Ezra
The Dissenters claim that the passage one may not take for security the lower millstone, nor the upper millstone is juxtaposed to the previous verse on account of “gladden his wife” [: 5], and that it is an allusion to sexual intercourse (in other words, he may not withhold sex) — but this is vacuous inanity. They offer for proof the verse “let my wife grind unto another” [Job 31: 10], which I have already explained. The true meaning is the literal one: It is forbidden for someone to take a millstone as security. The sentence fails to specify its subject, as in “he told Joseph” [Genesis 48: 1], “she bore her to Levi” [Exodus 26: 59], and many similar instances. In all cases the implicit subject is assumed: “ the speaker spoke to Joseph”, “ the mother bore her to Levi”, etc.
Rashbam
כי נפש הוא חובל, as per Onkelos, you would deprive the debtor of his source of legitimate income.