What is the ruling on selling cows for sacrifice by agreeing on the price per kilogram, paying part of the price, and leaving the cow with the merchant until two days before Eid to receive it after weighing and paying the remaining price? What are the rulings on guarantee in this sale if it is valid? What are the permissible forms if it is not valid, given the difficulty for the buyer to take possession of the cow at the time of purchase?

It is not permissible to purchase the sacrificial animal in the manner mentioned, because a sale is only valid if the price is known at the time of the contract. This is due to the prohibition by the Messenger of Allah, peace and blessings be upon him, of bay' al-gharar (definition) (a sale involving excessive uncertainty or risk), and because in this method, the price is not known until the animal is weighed. Furthermore, paying an advance with a promise is not permissible, because it constitutes a loan, and it is not lawful to combine a loan with a sale.

In the event that the sale is invalid, the cow remains the property of the seller and is under his guarantee.

A permissible purchase can be made after knowing the weight of the animal and its price. Then, it can be left with the seller for him to care for it in exchange for a fee, provided that its feed and expenses are borne by the buyer, and it remains under his guarantee. Alternatively, the buyer can promise to purchase without paying an advance, and then make a valid purchase at the appropriate time.