Cancellation of sale

You shall tell him that now you are not interested to sell the property and you shall repay the amount of sale which was taken by you under proper acknowledgment. 

In addition to the above expert views, I am of the opinion that you should file a civil suit to cancel the transaction.

Better settle the issue amicably .you entered into oral agreement with buyer and in pursuance of oral contract you received part payment and now you want to cancel the cotract without any reason  in such circumstances  buyer may file suit for specific performance of oral contract against you and you would have to face consequences and has to execute sale deed in favour of buyer.