Parashas Vayeira · Passuk 18:27
And Avraham answered and said, “Behold now, I have taken upon myself to speak to my Lord, though I am but dust and ashes.”
Torah Temimah points to Sotah 17a.
TT lemma: עפר ואפר.
English: “Dust and ashes.” Rava expounded: In the merit of Avraham’s saying “I am but dust and ashes,” his children merited two commandments—the ashes of the red heifer and the dust of the sotah.
Derash on the verse (Bavli sugya) — not a formal named middah of the 13. A statement of humility is linked measure-for-measure to later ritual substances.
Because Avraham called himself dust and ashes, Israel received the mitzvot of the ashes of the para adumah and the dust used in the sotah ritual.