TT #1 · Parashas Vayeira · Passuk 18:1
Hashem appeared to him by the terebinths of Mamre; he was sitting at the entrance of the tent as the day grew hot.
Torah Temimah points to Sotah 14a. E-Daf · Sefaria — Sotah 14a
TT lemma: וירא אליו ה'.
“And Hashem appeared to him.” From here we learn that it is the way of the Holy One, blessed be He, to visit the sick.
Derash on the verse (Bavli sugya) — not a formal named middah of the 13. The appearance of Hashem after the milah is read as a visit to the convalescent.
Visiting the sick is an imitation of Hashem’s own conduct: just as He appeared to Avraham while he recovered from circumcision, so we are obligated to visit the ill.