On surplus-value coming free to the capitalist,
"The circulation mechanism, however, has shown if the capitalist class casts money into circulation to be spent as revenue, it withdraws this same money again from circulation, and so the same process can always begin anew; considered as a capitalist class, therefore, it remains now as before in possession of this sum of money needed for the realization of its surplus-value. If the capitalist not only withdraws surplus-value from the commodity market in the form of commodities for his consumption fund, but at the same time the money with which he buys these commodities flows back to him, he has evidently withdrawn the commodities from circulation without an equivalent. They cost him nothing, even though he pays for them with money. If I buy commodities for one pound sterling, and the seller of these commodities gives me back my one pound in exchange for a surplus product that costs me nothing, then I have obviously received the commodities for nothing. The constant repetition of this operation, in no way alters the fact that I constantly withdraw commodities and constantly remain in possession of the one pound, even though I part with it temporarily in order to obtain these commodities. The capitalist constantly receives this money back as the realization of surplus-value that cost him nothing."(Capital, Volume II, pp550/551, Penguin Classics edition).