What is the 'arabun and what is its ruling?

Question:
This is the owner of a real estate office, Shaykh Salih. He says: We work in buying and selling land, so what is the criterion for the 'arabun? And if the sale is not completed, is the 'arabun returned?

Answer:
The 'arabun is that the contract includes an option. The sale is completed, but there is an option for a known period. The seller takes the 'arabun to ensure the buyer's commitment to the sale. If he is committed, he completes the price for him. If he abandons the sale, the 'arabun belongs to the seller. This is the position of Imam Ahmad, because 'Umar (may Allah be pleased with him) appointed someone to buy a house for the prison in Makkah. The agent bought the house for the prison on the condition that he would consult 'Umar, and he paid him an 'arabun. 'Umar approved that, the payment of the 'arabun, and the exception for consulting the Caliph. There is no harm in that. Yes.