Amir bhai is right. There is no such circular where intraday trading is considered as normal business income except in case of futures & options if routed through Recognised Stock exchange are non speculative business and the recognised stock exchnages are BSE, NSE & MCX stock exchange.
And sidharth even private limited companies can enter into speculative transactions.
Also there is a explanation to Section 73 which is deeming section to treat even delivery in shares as speculative transaction which is reproduced here:
73[Explanation.—Where any part of the business of a company (74[other than a company whose gross total income consists mainly of income which is chargeable under the heads “Interest on securities”, “Income from house property”, “Capital gains” and “Income from other sources”], or a company the principal business of which is the business of banking or the granting of loans and advances) consists in the purchase and sale of shares of other companies, such company shall, for the purposes of this section, be deemed to be carrying on a speculation business to the extent to which the business consists of the purchase and sale of such shares.]