Chullin 131 - One Who Damages or Eats the Kohen's Gifts
We learned that the foreleg, jaw, and abomasum of a slaughtered animal are a kohen's portion and should be given to him. However, Rav Chisda said that if one damages or eats these gifts, he does not have to pay. That is because the Torah said "This shall be his due" - meaning, only while "this" due is extant. The Talmud challenges Rav Chisda's ruling seven times, but Rav Chisda defends it each and every time.
For example, if a person of means runs out of funds while in travel, he is allowed to take the poor people's portion, that is, grain that fell, was forgotten, or remained at the corners of a field and was designated by the Torah for the poor. Still, when he comes back home, he needs to send the money to the poor people of that place, in order to repay them. By the same token, one should repay the kohen for his gifts that he damaged or ate!? Rav Chisda answers that to repay the poor is a decent act, but not a requirement, and the same goes for the kohen's gift.
Art: Alessandro Sani - A Gift From Grandpa