Diogenes Laertius on the Skeptics

The skeptics, then, were constantly engaged in overthrowing the dogmas of all schools, but enunciated none themselves; and though they would go so far as to bring forward and expound the dogmas of the others, they themselves laid down nothing definitely, not even the laying down of nothing. So much so that they even refuted their laying down of nothing, saying, for instance, “We determine nothing,” since otherwise they would have been betrayed into determining… (D.L. IX 74).

Lives of Eminent Philosophers
Diogenes Laertius