Shevuot 22 - Oath Not To Eat
If one swore, "An oath that I will not eat," and then he ate and drank, he is liable for only one offering. But if one swore, "An oath that I will not eat and that I will not drink," and then he ate and drank, he is liable to two offerings.
If one swore, "An oath that I will not eat," and then he ate prohibited foods, such as animals or foul that were not slaughtered correctly, unkosher fish, seals, frogs, flies, bees, mosquitoes - he is liable. Rabbi Shimon exempts him because he swore to do something he is already obligated to do, and his new oath did not take effect.
Art: Sea Food by Giacomo Ceruti
