Section 17(2)(c) in The Reserve Bank of India Act, 1934
(c)the purchase, sale and rediscount of bills of exchange and promissory notes drawn and payable in India and bearing the signature of a scheduled bank, and issued or drawn for the purpose of holding or trading in securities of the Central Government or a State Government and maturing within ninety days from the date of such purchase or rediscount, exclusive of days of grace;