Section 40A (3) says "No deduction is allowed in respect of which a payment or aggregate of payments exceeding rupees twenty thousand (reduced to 10000/- wef 01.04.2017) are made to a person in a day otherwise than by....." So you can pay a single bill exceeding Rs 10000 in cash to the same party on different dates but not on the same date. Also note that there are no compliances or penalties for making cash payment of more than Rs 20000. Only consequence is that your expenses will be disallowed. In case of part payment in cash exceeding Rs 10000 the disallowance will be limited to the extent of cash payment only.