From Value, Price and Profit (1865), with emphasis added:
It is perfectly true that, considered as a whole, the working class spends, and must spend, its income upon necessaries. A general rise in the rate of wages would, therefore, produce a rise in the demand for, and consequently in the market prices of necessaries. The capitalists who produce these necessaries would be compensated for the risen wages by the rising market prices of their commodities. But how with the other capitalists who do not produce necessaries? And you must not fancy them a small body. If you consider that two-thirds of the national produce are consumed by one-fifth of the population — a member of the House of Commons stated it recently to be but one-seventh of the population — you will understand what an immense proportion of the national produce must be produced in the shape of luxuries, or be exchanged for luxuries, and what an immense amount of the necessaries themselves must be wasted upon flunkeys, horses, cats, and so forth, a waste we know from experience to become always much limited with the rising prices of necessaries.
Via [fn3], h/t ejh.