Source, in full
One of the statements presenting what has become known as "Moore's paradox, from a famous lecture concerning logical inconsistency in 1942, as quoted in Reason in Theory and Practice (1969) by Roy Edgley, p. 71; in which he also stated "It is not raining, but I believe that it is." These sentences are not logically contradictory, and yet it seems that no one could make a true assertion by sincerely speaking them. It is reported that Ludwig Wittgenstein, on hearing of Moore's lecture, went to Moore's house in the middle of the night to ask him to repeat it, and considered the problems presented by it Moore's greatest contributions to philosophy.
Notes from Wikiquote
It is raining but I don't believe that it is. | As quoted in Directives and Norms (1968) by Alf Ross, Brian Loar, p. 27. | It is raining but I don't believe that it is raining. | As quoted in Foundations of Illocutionary Logic(1985) by John R. Searle and Daniel Vanderveken, p. 19.