See Columbia Accident Investigation Board report, page 127. Hoot Gibson's comments are on p. 31 of the second PDF: http://www.nasa.gov/columbia/caib/PDFS/VOL1/PART02.PDF

Most of the testimony given to the CAIB were sealed (very controversial move), so that's the only quote we have from him. However, he later gave an interview: http://www.spaceflightnow.com/shuttle/sts119/090327sts27/

Another account can be found in Mike Mullane's memoirs, Riding Rockets. Mullane was a mission specialist on STS-27, and operated the Canadarm during the tile inspection. He says that he kept thinking about the tiles, and had trouble sleeping. Hoot Gibson advised him: "No reason to die all tensed up."

Remember -- STS-27 was the second mission after the Challenger explosion. Not enough time yet for complacency to have set in. In addition, Mike Mullane had an it-was-absolutely-not-an-affair-we-were-just-friends relationship with Judy Resnick. So he knew very personally just how dangerous the Shuttle could be.

I'd never heard about this before, thanks very much for sharing. This is remarkable.