Upvote:2
There is no doubt the quote is widely attributed to him. Several sources I checked give him credit:
Some sources are not so sure Voltaire spoke the original:
I did not find a reference to any of Voltaire's works that may have contained the quote.
Your safest course, it seems to me, is that, in the opinion of many, the quote is Voltaire's; however, the actual source has not yet been verified.