TT #48 · Parashas Vayeira · Passuk 18:33
And Hashem went His way when He had finished speaking to Avraham, and Avraham returned to his place.
Torah Temimah points to Derech Eretz Rabbah 5 (and parallel).
TT lemma: וילך ה'.
“And Hashem went.” It was taught: A person should never take leave of his teacher or his friend unless he first obtains permission from him. We learn proper conduct from the Omnipresent, as it is said, “And Hashem went when He had finished speaking to Avraham”—as if to say, “Behold, I am taking leave of you.”
Derash on the verse (baraita / Derech Eretz) — not a formal named middah of the 13. Divine behavior teaches human etiquette.
One should not depart from a teacher or friend without first taking leave; Hashem Himself modeled this by “going” only after finishing the conversation with Avraham.