On Purim and all the days of Hanukkah, a curious piece of liturgy is added to both the blessing after meals and the thrice-daily silent prayer. The two festivals have in common that each is of entirely rabbinic invention and celebrates a miraculous deliverance from Gentile monarchy. There is a specific version for Hanukkah and a parallel one for Purim, but the two share the same opening lines, the first two words of which, al ha-nissim, give the prayer its name (I’ve used the Sephardi version here, but the wording in the Ashkenazi liturgy is nearly identical):