“Labour is the source of all wealth, the political economists assert. And it really is the source -- next to nature, which supplies it with the material that it converts into wealth. But it is even infinitely more than this. It is the prime basic condition for all human existence, and this to such an extent that, in a sense, we have to say that labour created man himself.”

Vol. I, Ch. 15 (last sentence), pg. 556.
(Buch I) (1867)

Shadow Secretary of State for Education and Science
Source: Interview with Sam Aaronovitch for Marxism Today (June 1983) http://banmarchive.org.uk/collections/mt/pdf/83_06_06.pdf

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.

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

Future Proofing You (2021)

Speech to the Classical Association (8 January 1926), quoted in On England, and Other Addresses (1926), p. 105.
1926
Context: A character founded on pietas and gravitas had its roots in truth, and I am proud to think that the English word has been held in no less honour than the Roman... It is from Ammian, who wrote while the legions were leaving Britain, that we learn that the Roman word could no longer be trusted. That is to me a far more significant portent than the aggregation of the population in cities, the immense luxury, and the exhaustion of the permanent sources of wealth, all of which combined to sap that very character whose continued existence was necessary for the life of the State.

As quoted in "Socialism is So Hot Right Now" https://www.commentarymagazine.com/articles/socialism-hot-right-now/ (17 September 2018), by Jonah Goldberg, Commentary
1990s

The Abolition of Man (1943)

Source: A History of Economic Thought (1939), Chapter I, The Beginnings, p. 41 ( See also.. 1 Corinthians 3 - 9.. KJV )