Full Idea
The liar paradox of Eubulides says 'if you state that you are lying, and state the truth, then you are lying'.
Gist of Idea
If you say truly that you are lying, you are lying
Source
report of Eubulides (fragments/reports [c.390 BCE]) by R.M. Dancy - Megarian School
Book Reference
'Encyclopedia of Classical Philosophy', ed/tr. Zeyl,Donald J. [Fitzroy Dearborn 1997], p.328
A Reaction
(also Cic. Acad. 2.95) Don't say it, then. These kind of paradoxes of self-reference eventually lead to Russell's 'barber' paradox and his Theory of Types.