Seller keeping advanced payment after canceling a sale
Q: I have done an agreement for sale of property with a person and got X amount as advance payment. Remaining have to paid within 3 months. There was a clause in the agreement that if the buyer is unable to pay the remaining amount or backs off from the deal, I will keep the advance payment as a penalty. (There was another clause for the seller also if he backs off, he will give double of advance taken to buyer).
Now the buyer is backing off and wants to cancel the deal due to unavailability of remaining payment. Is the penalty amount of advance payment halaal for me to keep?