[If] he bought a first-born animal for his son’s [wedding] feast or for the festival, and he did not need it, he is permitted to sell it. Trappers of wild animals, fowl, or fish, who chanced upon unkosher species are permitted to sell them. R’ Yehudah says: Even someone to whom such [an animal] happened to come his way may take it and sell it, provided that he does not make a specialty of this. But the Sages forbid it.