“If your mother says she loves you, get a second source.”
“If your mother says she loves you, get a second opinion.”

One place attributes the latter to Dan Rather; another to the movie Primal Fear. Clearly the saying predates both of them.

Other variants:
“If your Mother says she loves you, get two independent sources of confirmation.”
“If your Mother says she loves you-get it verified.”
“Even if your mother says she loves you, get two references.”

So: who said this first? where? when? and what did they say?