Full Idea
It is inconceivable that mind and body should have any influence on one another, and it is unreasonable simply to have recourse to the extraordinary operation of the universal cause in a matter which is ordinary and particular.
Clarification
By 'universal cause' he means God
Gist of Idea
Mind and body can't influence one another, but God wouldn't intervene in the daily routine
Source
Gottfried Leibniz (Discourse on Metaphysics [1686], §33)
Book Reference
Leibniz,Gottfried: 'Philosophical Writings', ed/tr. Parkinson,G.H.R. [Dent 1973], p.42
A Reaction
Leibniz was the ultimate intellectual contortionist! Here he is rejecting Cartesian interactionism, and also Malebranche's Occasionalism (God bridges the gap), in order to prepare for his own (daft) theory of what is now called Parallelism.