TT #12 · Parashas Vayeira · Passuk 18:4
Let a little water be brought, and wash your feet, and recline under the tree.
Torah Temimah points to Bava Metzia 86b. E-Daf · Sefaria — Bava Metzia 86b
TT lemma: ורחצו רגליכם.
“And wash your feet.” They said to him, “Do you suspect us of being Arabs who bow down to the dust of their feet? Yishmael has already gone forth from him.”
Derash on the verse (Bavli sugya) — not a formal named middah of the 13. The request to wash feet is read against the background of contemporary idolatrous practice.
Avraham’s offer of water for the feet was understood by the angels as a precaution against possible idolatry; they protested that such suspicion was unfounded.