Rabbi I have a question which arose on this Purim past. I had the honor of shlishi when I completed the the brach I asked the chazan
to say “el molly rachamim” at which time he said that one cannot
say it on Purim.
Please reply,
Answer:
The “El Maley Rachamim” prayer is not said on days that Tachanun is omitted, and this includes Purim.
See Iggros Moshe, Orach Chaim 2:74, concerning the question of why Shabbos special in this respect.
Best wishes.