Cash Receipt Window: Stop user to delete receipts.

Requirement: 

We are looking for a way to disable the “Delete” functionality on Cash Receipt Entry window, like when closing the window a message pop-up asking to save or delete the receipt will not allow user to select delete. From field level security I had already disabled “Delete” button. But for pop-up notifications I am unable to block it. Can we do any customization for this ?

Solution: Small customization was done for blocking the delete functionality for certain users, users will not able to delete cash receipts and need to save the changes for existing cash receipts. Users with disabled functionality was identified by user class id assigned to users.

Estimated Time: 10 Hours.