TT #19 · Parashas Vayeira · Passuk 18:8
He took curds and milk and the calf that he had prepared, and set them before them; and he stood over them under the tree, and they ate.
Torah Temimah points to Bava Metzia 86b. E-Daf · Sefaria — Bava Metzia 86b
TT lemma: והוא עומד עליהם.
“And he stood over them.” There was an incident with Rabbi Eliezer, Rabbi Yehoshua, and Rabbi Tzadok who were reclining at the wedding feast of Rabban Gamliel’s son, and Rabban Gamliel himself stood and served them drink… He said to him, “We have found one greater than he who served: Avraham was the greatest of his generation, and it is written of him, ‘And he stood over them.’”
Derash on the verse (Bavli sugya) — not a formal named middah of the 13. Avraham’s personal service becomes the model for a host of high stature serving his guests.
Even a person of the highest stature may (and should) personally serve his guests, as Avraham stood and attended the three men under the tree.