In Shabbos 24a there is a discussion about referring to Hanukkah when saying Birkat Hamazon. Part of the discussion centers around saying you wouldn't mention it because Hanukkah is mi d'rabonim. Why didn't they use the other holiday not from Torah, Purim, as an example?
Actually, the same question of whether to mention Al ha'Nisim in Birkas ha'Mazon applies equally to Purim! (The Gemara does not ask the question with regard to Purim because the practice to say Al ha'Nisim on Purim is not written anywhere in the Talmud.) Indeed, TOSFOS here (DH d'Tani) understands to Gemara's question to apply to both Purim and Chanukah.