Recently I was listening to a defense of the observation of the Sabbath, and within it the speaker quoted Voltaire as saying something like:
If you want to kill Christianity, you must abolish Sunday.
I've found this quote in a number of places both online and in print, such as in the International Standard Bible Encyclopedia, IV, 159, but so far I haven't found an actual reference to the writings of Voltaire. Sadly I don't read French, so I wouldn't know how to best search for this quote in the original language either.
Did Voltaire actually say something like this? And if so, where/when?