Full Idea
The cause of good is positive, but evil is a defect, that is, a privation or negation, and consequently, it arises from nothingness or nonbeing.
Gist of Idea
Evil is a negation of good, which arises from non-being
Source
Gottfried Leibniz (Dialogue on human freedom and origin of evil [1695], p.114)
Book Reference
Leibniz,Gottfried: 'Philosophical Essays', ed/tr. Arlew,R /Garber,D [Hackett 1989], p.114
A Reaction
He goes on to illustrate his idea from mathematics. He is modifying Augustine's view that evil is an absence of good, by adding nonbeing as the driving force behind it. Doesn't sound very persuasive to me.