The Mishnah stated, "One may not fuel his oven or stove with it'' (Chametz after the time).

Question: What is the din if someone transgressed and did so?

Answer: It should follow the din of the Mishnah (that discusses an oven that as fueled with shells of orlah) - If it was a new oven (that this fueling caused the completion of the oven), one must break it; if it was an old oven, one must allow the oven to cool off (in order to prevent further use of this prohibited heat).

Beraisa (R' Yehudah): Chametz may only be destroyed through burning. It is a Kal va'Chomer - If pigul and nosar, which do not have a prohibition of Bal Yera'eh and Bal Yimatzei, may only be burned; certainly Chametz, which has a prohibition of Bal Yera'eh and Bal Yimatzei, should only be burned!

(Chachamim respond): Any Kal va'Chomer expounded that begins as a stringency but ultimately leads to a leniency is not a valid Kal va'Chomer. If he does not have a way of lighting a fire, will he sit and refrain from destroying the Chametz? The Torah says (Shemos 12,15), "You shall destroy Se'or from your houses''?!

Another similar case (R' Yehudah): (Vayikra 12,2) "When a woman conceives and gives birth to a boy'' - what is it coming to teach? Since it says further "and she will be impure for seven days...and on the eighth day he shall be circumcised'', one can only learn that if he came out alive, she is impure for seven days. From where do we learn that if he comes out dead, it makes the mother impure for seven days?

The Beraisa answers (R'Yehudah): I will make a Kal va'Chomer - If he comes out alive, where neither the mother nor others who come into the same room will become impure from him (tumas ohel) for seven days, but nevertheless he makes the mother impure (tumas leidah) for seven days; if he comes out dead, where both the mother and others who come into the same room will become impure for seven days, certainly he will make her impure for seven days!

(Chachamim respond): Any Kal va'Chomer expounded that begins as a stringency but ultimately leads to a leniency is not a valid Kal va'Chomer. If a living baby will cause the mother to have days of purity (after giving birth to a boy, the mother is given 40 days where her blood is pure and 80 days after having a girl), will a dead baby cause the mother those days of purity? Since you cannot expound it through a Kal va'Chomer, th]e Torah stated "zachar'' - "a male'', to include a dead baby [in the laws of tumas leidah].