How to put Credit hold for customers that does not have terms and credit limit on invoice transactions but not on cash sales.

Assuming that you have set your Customer Credit Limit Handling (Setup>Accounting>Accounting Preferences) to Enforce Holds and on the customer record the Hold was set to Auto, once a customer reaches the credit limit, sales invoices should not be saved.  

In order to enforce holds for customers that does not have terms and credit limit for invoice transactions and at the same time can save and process cash transaction, make sure to set the Credit Limit to zero on the customer record.  If the Credit Limit is null, you can still save the invoice and enforce hold will not work.