Actually this contact when you made you would have given a time frame for the contact this agreement to sell by this agreement the purchaser have the liberty to not to go for a change because of the financial however at this point of time you have the option that you have to send a legal notice to him to provide the detail of finances if he has arranged to quash the contract in case he is not able to find out the finance.
I believed due to this clause he is taking benefit and delaying the sale process.