TT #19 · Parashas Toldos · Passuk 26:5
inasmuch as Avraham obeyed Me and kept My charge: My commandments, My laws, and My teachings.”
Torah Temimah points to Yoma 28b. E-Daf · Sefaria — Yoma 28b
Rava said: Avraham our father even observed the laws of eruv tavshilin, as it is said “and My teachings” — one written Torah and one oral Torah.
Custom (Bavli — Avraham observed even eruv tavshilin)
Avraham observed even rabbinic decrees such as eruv tavshilin; the plural “My teachings” is the source.