1. Al Ha-nissim (“for the miracles”) is inserted in Birkas Hamazon of Purim. Even if one began the Purim feast during the day of Purim and only finished it at night, he nevertheless recites Al Ha-nissim because the obligation is determined by the beginning of the meal. If the person prayed Ma’ariv the night following Purim before reciting Birkas Hamazon, some say that he does not insert Al Ha-nissim (Shulchan Aruch 695).
2. One who forgets to insert Al Ha-nissimin Birkas Hamazon does repeat Birkas Hamazon but adds at the end of Birkas Hamazon the formula: “May the Compassionate One perform for us miracles and wonders as He performed for our forefathers in those days, at this time. In the days of Mordechai and Esther…” (ibid.).
