“Labour, upon whichever of those operations it be bestowed, is productive, because it concurs in the creation of a product. Thus the labour of the philosopher, whether experimental or literary, is productive; the labour of the adventurer or master-manufacturer is productive, although he perform no actual manual work; the labour of every operative workman is productive, from the common day-labourer in agriculture, to the pilot that governs the motion of a ship.”

Source: (1776), Book II, Chapter III, p. 377.

Source: The Limits To Capital (2006 VERSO Edition), Chapter 11, Theory Of Rent, p. 347

Vol. I, Ch. 11, pg. 336.
(Buch I) (1867)

Source: A Treatise On Political Economy (Fourth Edition) (1832), Book I, On Production, Chapter VIII, p. 91

The Collected Works of Abraham Lincoln edited by Roy P. Basler, Volume I, "Fragments of a Tariff Discussion" (1 December 1847)
1840s

Source: (1776), Book I, Chapter I, p. 7

Grundrisse (1857-1858)
Source: Notebook VII, The Chapter on Capital, pp. 628–629.

Vol. I, Ch. 2, pg. 99.
(Buch I) (1867)

Notebook VII, The Chapter on Capital, pp. 628–629.
Grundrisse (1857/58)
Context: The development of fixed capital indicates in still another respect the degree of development of wealth generally, or of capital…
The creation of a large quantity of disposable time apart from necessary labour time for society generally and each of its members (i. e. room for the development of the individuals’ full productive forces, hence those of society also), this creation of not-labour time appears in the stage of capital, as of all earlier ones, as not-labour time, free time, for a few. What capital adds is that it increases the surplus labour time of the mass by all the means of art and science, because its wealth consists directly in the appropriation of surplus labour time; since value directly its purpose, not use value. It is thus, despite itself, instrumental in creating the means of social disposable time, in order to reduce labour time for the whole society to a diminishing minimum, and thus to free everyone’s time for their own development. But its tendency always, on the one side, to create disposable time, on the other, to convert it into surplus labour...
The mass of workers must themselves appropriate their own surplus labour. Once they have done so – and disposable time thereby ceases to have an antithetical existence – then, on one side, necessary labour time will be measured by the needs of the social individual, and, on the other, the development of the power of social production will grow so rapidly that, even though production is now calculated for the wealth of all, disposable time will grow for all. For real wealth is the developed productive power of all individuals. The measure of wealth is then not any longer, in any way, labour time, but rather disposable time. Labour time as the measure of value posits wealth itself as founded on poverty, and disposable time as existing in and because of the antithesis to surplus labour time; or, the positing of an individual’s entire time as labour time, and his degradation therefore to mere worker, subsumption under labour. The most developed machinery thus forces the worker to work longer than the savage does, or than he himself did with the simplest, crudest tools.