Leonard Ravenhill quotes

I love this quote by Leonard Ravenhill; "I have this in black and white-- where the Communists said in their manifesto: Christianity is certainly more powerful than anything we have. Jesus Christ can do more than Karl Marx, but the (professing) Christians don't believe it, and secondly, they won't sacrifice for it."
My problem is I cant find the documentation for this anywhere. Does anyone know where I can find the documentation for this. I want to document it, before I use it as a sermon illistration.
Thanks and God bless,
Pastor Vic