Bava Metzia 100 - Disputes Between Buyer and Seller
If one exchanged a cow for a donkey in a barter exchange and the cow calved, and the seller says that the cow calved before he sold her, and therefore the offspring is his, and the buyer says that it calved after the sale, and the calf is his - they divide the value of the calf.
But let’s see in whose possession the calf is now - and the burden of proof would be on the other side! - The cow is in the meadow. But let us leave it with the original owner - the seller! This ruling is authored by Sumchos, who always divides the money whose ownership is in doubt.