Now for your question. The answer is pure accident. I walked right into it.

9 seconds sound clip from the A Star is Born classic radio play.

You can hear this line at 00:52:46 in the radio play.

Quote context

[...]

- The founder and guiding light of that theater is here tonight - one of the greatest showmen and best friends that motion pictures have ever had - Sid Grauman.

- How did you happen to get that idea of the hand and footprints?

- Well, before answering that, I'd like to say something you overlooked.

- That it was your picture, 'The King of Kings,' that opened the Chinese Theatre.

- It was a great break for me.

- Now for your question. The answer is pure accident. I walked right into it.

- While we were building the theater I accidentally happened to step in some soft concrete, and there it was.

- So I went to Mary Pickford immediately. Mary put her foot into it.

- And so became the first to sign your concrete autograph album, eh?

- Yes, along with Norma Talmadge and Douglas Fairbanks.

- The latest who have done so are William Powell and Myrna Loy, who used to dance in my prologues.

- While most of us have heard of your theatre and footprints, few people realize that you've helped scores of players on their way to fame...

[...]