R. Moshe Feinstein on Swearing to Violate Rabbinic Prohibitions (10 Iyar)
אגרות משה יורה דעה א:קלט-קמ 10 Iyar (5687) 1927
When we take an oath, we can promise to do or not do something that affects our Torah observance-- what if someone takes an oath not to eat matzah on Pesach? Do such oaths take effect? When yes, when no, and does the question of whether the halachic issue is from Torah law or a Rabbinic ordinance affect our reaction?