Who said it's not what you say but how you say it?

I researched this on google and nothing came up except a bunch of Amazon links.... so I think no one originally came up with this quote, but it's been said and repeated throughout the generations.

But, I'll tell you right now, my mom and dad have said it a thousand times! ;)

It is not what you say that matters but the manner in which you say it; there lies the secret of the ages. William Carlos Williams (1883 - 1963)