That's what I say

That's what I say.

Inf. I agree with what was just said. Tom: We've got to get in there and stand up for our rights! Mary: That's what I say. Bob: They shouldn't do that! They should be put in jail! Mary: That's what I say!
See also: say, what
References in classic literature ?
God forbid that we should ever turn back to those times; that's what I say, Jerry.
That's what I say, and I've said it many a time; but there's nobody 'ull ventur a ten-pun' note on their ghos'es as they make so sure of.
All I say is," answered Agafea Mihalovna, evidently not speaking at random, but in strict sequence of idea, "that you ought to get married, that's what I say.