What is the ruling on selling five sheep if one of them perishes while with the buyer after a period of time, and is the buyer obligated to pay the price for all five or for the remaining four?

Since the buyer has taken possession of the sheep, he is obligated to pay the price to the seller. The jurists have agreed that if the sold item is damaged after possession, the sale is not invalidated, and the destruction is borne by the buyer, who is still liable for the price, whether the damage was caused by a natural disaster, by the sold item itself, or by the buyer.