Siman 224

Our sages, of blessed memory, said in Ketubot [76b] that anyone in whose domain a doubt [of disadvantage] arose must bring proof. How so? One who exchanges a cow for a donkey, and the owner of the donkey pulled the cow, but the owner of the cow did not manage to pull the donkey before the donkey died, or was stolen, or was lost, and it is not known when it died—whether before the pulling of the cow or afterward—the owner of the cow must bring proof. For since the donkey was acquired by him wherever it may be via the pulling of the cow by the owner of the donkey, as explained in siman 195, the donkey is in the domain of the owner of the cow, and he must bring proof. And thus said the sages of France and Ashkenaz, that anyone in whose domain a doubt arose must bring proof, whether to extract money or to retain money in his possession [the Rosh]. And since the owner of the donkey pulled the cow, the donkey is considered as standing in the domain of the owner of the cow, even though it is still in the domain of the previous owner. And one should not raise a difficulty: if so, why do we rule that when the buyer seized the cow and it gave birth, the seller must bring proof, as explained in the previous siman? Why do we not say that since it is in his domain, he must bring proof? For in truth, they are not comparable; for there, since it is to his benefit that he merit the offspring, certainly since he is the possessor, he merits according to the law of all presumptions of possession, and the one who comes to extract from him must bring proof. But when the possession is to his disadvantage, and on the contrary, his benefit is when we say that the defect was not in his possession, it is impossible to say that he should merit because of his possession. On the contrary, his merit is when we say that the defect was not in his possession, and therefore we rightly say that since the doubt arose in his domain, he must bring proof that the defect was not yet in his domain. And if he does not bring proof, the seller shall swear that he did not know of its death at the time he pulled the cow, and also that it was not ill in a manner that would constitute ona'ah, and he is exempt. And our teacher, the Rema, ruled accordingly.

But our teacher, the Beit Yosef, transcribed the words of the Rambam in chapter 20, who wrote: Anyone in whose domain a doubt was born, the burden of proof is upon him. How so? One who exchanges a cow for a donkey, and the owner of the donkey pulled the cow, but the owner of the cow did not manage to pull the donkey before the donkey died—the owner of the donkey must bring proof that his donkey was alive at the time of the pulling of the cow, and so too in any similar case. Thus far his words. And this is the approach of the Rif as well, that "domain" refers to the place where the donkey is standing when the defect was born, such that the owner of the domain must bring proof because we say "here it is found and here it was." Therefore, there is one who says that when it dies in a marsh or in the domain of another, the owner of the cow must bring proof [Sma], and so wrote the Tur [and in the book Imrei Lekaach Tov, siman 43, we explained this with the help of Heaven].

A needle that was found in the thickness of the beit hakosot and perforated it with a through-hole, if a drop of blood is found upon it, it is known that it became treifah before slaughter. Therefore, if the wound has scabbed over, meaning a thin skin has formed over the wound, it is known that this animal became treifah three days before slaughter, for in less than this it would not have scabbed. Consequently, if he slaughtered it within three days of its purchase, it is known that it became treifah in the possession of the seller. If the wound did not scab over, or if he slaughtered it after three days from its purchase, this is a doubt as to when it became treifah; for even when it has not scabbed, it is possible that it became treifah long ago. Since it is a doubt, it is upon the butcher to bring proof that it became treifah before his purchase, for the doubt arose in his domain, and we say "here it was found, here it was." If he did not bring proof, he must pay the money to the seller even if he has not yet given the funds, and we extract it from him and give it to the seller. For it is a great principle regarding a defect that is found, where the buyer desires to void the transaction, that in whichever domain it was found, it is upon him to bring proof, whether to extract or to retain. If the pulling and the slaughter were not in the domain of the butcher but in another's domain or in a simta, according to the opinion of the Rosh, it is upon the butcher to bring proof; and according to the Rambam, since the defect is not in the domain of the butcher, he does not need to bring proof [Taz]. And one must see who is the one coming to extract, for if the buyer has not yet given the money, the owner of the animal is called the extractor and the proof is upon him. And in siman 232, section 24, it will be explained that sometimes it is upon the buyer to bring proof even when he is not coming to extract, such as when there is a chazakah or a majority that assists the seller, see there.

An incident occurred involving Reuven, who exchanged his horse for the wine of Shimon, and when Shimon pulled the horse, the wine was immediately acquired by Reuven according to the law of chalifin. In the midst of this, an extortionist came and took the horse from Shimon with the claim that the horse was stolen from him, yet he brought no proof for this. Shimon wanted to void the exchange and retain his wine. The great authorities ruled that if Reuven admits that the horse was stolen from the extortionist, it is a mistaken transaction and the wine remains in the hand of Shimon. However, if Reuven does not admit this, we say that the extortionist is lying and he must give the wine to Reuven, for his ill fortune caused it. Reuven does not even require an oath, for one does not swear regarding a claim of uncertainty when there is no basis for the matter [Gra]. The words of the extortionist without any proof are not called a basis for the matter, for presumably he is lying.