Pesachim 24 - Again, why is chametz is prohibited on Passover?
A student was sitting in front of Rabbi Shmuel bar Nachmani and retelling him the teachings of Rabbi Yehoshua ben Levi. He said, "How do we know that chametz is forbidden for all benefit on Pesach?"
Rabbi Shmuel exclaimed in amazement, "We know that from ‘do not eat’ prohibition. Why do we need anything else?" The student then showed him how according to other views of Rabbi Yehoshua this derivation would not work. Rabbi Shmuel was convinced, and the student continued, "From ‘all invalid sin offerings you should burn in fire.’" Now, this command is not needed, because the offering in question was already burned in fire. Here we see a new fundamental rule: if there is a commandment, which seems unneeded and repetitive, one can apply it to another area of law. For example, if we don’t need to know that a sin offering should be burned, we can apply it to chametz on Passover and require it to be burned rather than used for benefit.
The Talmud then finds yet another, different way to derive that any use of chametz is prohibited on Passover.
Art: A Notty Question by Louis Charles Moeller