Who said, "Your first million words don't count?"

I’ve long held that Robert Heinlein once gave this sage advice to aspiring authors: “Your first million words don’t count.” My wife recently repeated this to a third party, but insisted that it was originally spoken by Ray Bradbury. In an effort to clear things up, I went online to discover the truth. Seems that Bradbury was the correct answer. As was Heinlein. I could find no authoritative source to provide an attribution. Any ideas?

I have a hard time seeing how it could be Heinlein, considering that he sold his first story the first place it was submitted to. Very much the exception, of course, but still, I can’t see him giving advice whose opposite worked out so well for him.

Looks like it was Bradbury, from Googling, but I can’t find a source.

ETA: Might also be Jerry Pournelle. Again, no source. Random site with it.

Except that’s not true. Yes, “Life-Line” sold first time out, but he had already submitted For Us the Living unsuccessfully to everybody but the University of Pitcairn Island Press, and had a number of other non-sales in his early years.

I believe it was Pournelle, but I can only remember reading it in one of his Chaos Manor columns in Byte magazine. I don’t remember if he was quoting someone else, or whether it was originally his. This half-quotation, which I can find in several places on the internet, seems to suggest it was his, but I don’t quite remember how it ended:

Ray Bradbury used to say this at speaking engagements in 1973. I was there, so my post is my cite.

Could he have been quoting someone else?

If he was, it was without attribution. I just wanted to add 1973 as a datapoint; if someone else finds an earlier cite, I suppose Bradbury could have heard it somewhere.

Hmm. Elmore Leonard notes a similar quote, which he attributes to John D. MacDonald here:

“John D. McDonald said that you had to write a million words before you really knew what you were doing.”