It provides that any expenditure incurred as a payment in sum of exceeding Rs.20000/- otherwise of paying with payee account cheque, demand draft or any transaction made by banks like RTGS, shall not be allowed as a deduction. However if payment is being made for hiring or leasing, the limit is 35000.
It also provides that the payment in a single day should not be exceeding Rs. 20000. It doesn’t mean the single payment shouldn’t 20000 but the aggregate amount should not exceed the limit. Some parties split high value payment into several cash payment for evasion of section 40A (3) a, so this rule is for evasion of payments.