Dear Sir,
Referring to Provisio to Sec. 140(3), it clearly mentions -
Provided that where a registered person, other than a manufacturer or a supplier of services, is not in possession of an invoice or any other documents evidencing payment of duty in respect of inputs, then, such registered person shall, subject to such conditions, limitations and safeguards as may be prescribed, including that the said taxable person shall pass on the benefit of such credit by way of reduced prices to the recipient, be allowed to take credit at such rate and in such manner as may be prescribed.
Hope it answered your query.