Tip Top Tailors Limited v. The Minister of National Revenue, 57 DTC 1232, [1957] CTC 309, [1957] S.C.R. 703 -- summary under Foreign Exchange

In 1947 the taxpayer, which anticipated the devaluation of the pound, arranged a line of credit with the London branch of a Canadian bank and arranged for the bank to pay its U.S. suppliers of cloth. When the pound was devalued in September 1949, the taxpayer promptly paid off the overdraft at a gain. Because the overdraft arose in the course of the taxpayer's business rather than as a separate financing transaction, the gain was realized on income account.