Parashas Yisro · Passuk 20:22
Chabad.org — English translation + Rashi
Torah Temimah points to Mechilta (verified).
Sefaria — Exodus 20:22
Sefaria — Mechilta
English: What is gazit? Stones that have been cut, upon which iron has been waved. … The altar was created to lengthen a person’s years, and iron to shorten them; therefore one may not wave that which shortens over that which lengthens.
In context: See the cited source for the full section.
Derash on the verse.
Iron, the instrument of death, may not be lifted over the altar, the instrument of atonement and life.