Correction: Chair Mao didn't say everything after all.
As Li pointed out, I had the wrong memory. I never aced any of these courses in my school days. BUT, I should have GOOGLED!!! :) That saying was published on May 11th, 1978. However, it was not proposed by Deng Xiaoping, despite the common perception. Deng only publicized it a lot. This is again a good example of Stigler's law of eponymy.