The Day the Jewish People Came Into Existence
Rabbi Sruly Bornstein
Why don't we say Tachnun on the 13th day of Nissan? Most of the month.. The Torah calls Erev Pesach a Yom Tov itself, so 13 is the day before. Avraham Avinu's bris was on the 13th of Nissan. Sugya: י"ג ניסן