Full Idea
The dialectic is often described in terms of thesis, antithesis, and synthesis - though this is not a Hegelian way of speaking. Hegel himself sometimes describes it in terms of negation and negation of the negation.
Gist of Idea
Hegel's dialectic is not thesis-antithesis-synthesis, but usually negation of negation of the negation
Source
report of Georg W.F.Hegel (Science of Logic [1816], I.i.i.C(c) p.150) by A.W. Moore - The Evolution of Modern Metaphysics 07.4
Book Reference
Moore,A.W.: 'The Evolution of Modern Metaphysics' [CUP 2013], p.173
A Reaction
A footnote says the first form of description only occurs once in Hegel's work. I am guessing that Marx is responsible for the standard misrepresentation.