> The quote "An alleged scientific discovery has no merit unless it can be explained to a barmaid." is popularly attributed to Lord Rutherford of Nelson in as stated in Einstein, the Man and His Achievement By G. J. Whitrow, Dover Press 1973. Einstein is unlikely to have said it since his theory of relativity was very abstract and based on sophisticated mathematics.[1]

Also, see the next answer for a more direct source. The list of misattribution is entertaining, too.[2]

[1] - http://skeptics.stackexchange.com/a/22409

[2] - https://en.wikiquote.org/wiki/Albert_Einstein#Misattributed