Sale deed

I am selling my flat. The buyer is paying 70% of the amount through bank loan, SBI. The buyer claims that as per the bank, sale deed has to be registered first, then he has to mortgage the property and after 3 to 4 days the bank will release the cheque to me. However, he says that details of the cheque will be mentioned in the sale deed at the time of registry. Is this okay? How can he mortgage the property without even making the payment to me?