Look them up yourself. Many "credible" gunwriters over the years have written about it. "Credible" people here have told you it is OK to do.
You are either being argumentative for the sake of it, or simply cannot fathom something not clearly outlined in a manual somewhere.
"Credible" people have been using .44 Spl loads in .44 Magnum brass for decades without issues. If that isn't good enough for you, don't do it. Besides, I could care less if you think it is a good idea, we are responding for the OPs sake, not yours.
If you think it is unsafe, tell the OP so and maybe even give a good reason or two why, then let them decide what advise they wish to take/not take in this thread, but arguing with other posters who disagree with you, who say it is OK, and demanding proof in a way satisfactory to you, is a waste of time.
Manuals show loads for the caliber, they don't go into downloading certain pistol calibers, so you are asking for the impossible, but you know that. Gunwriters and other experienced, safe, reloaders have been doing this since before I knew what reloading was. People here have shot thousands of .44 Spl loads in .44 Mag brass. And again, if you cannot see why it would be perfectly safe without a manual telling you so, it's a lost cause.