An Argument from authority is one in which a proposition is claimed to be true because an esteemed person says it is true. It is a fallacy in that it relies on the person's fame or reputation, rather than on logical arguments or Scientific, empirical evidence. We should accept expert opinion only if the experts know what they're talking about and as we all know experts frequently disagree.
"Albert Einstein believed in God. Are you saying that Einstein was wrong?" Incidentally Einstein used the word God as a metaphor for an impersonal force, he didn't believe in a personal God.