Letters 88.44

Parmenides maintains that nothing exists of all this which seems to exist, except the universe alone. Zeno of Elea removed all the difficulties by removing one; for he declares that nothing exists. The Pyrrhonean, Megarian, Eretrian, and Academic schools are all engaged in practically the same task; they have introduced a new knowledge, non-knowledge.

Seneca, Letters to Lucilius 88.44, translated by Richard Mott Gummere