The Mitzva to eat in honor of a Mitzva – Hilchot Chametz umatza 3:9
Before Pesach one must destroy all of the chametz in his possession. What happens if you left on a trip and forgot some chametz at home? The Rambam says that if you are traveling for a mitzvah then if you are unable to both return and destroy the chametz and also do the mitzva, then…