Here are some citations.
https://www.irs.gov/pub/irs-drop/n-14-58.pdf
https://www.irs.gov/Businesses/Guidance-for-Examiners-and-Ma...
Just look up "sham transaction" for plenty more. It's a very well established concept and doctrine. Nobody should be splitting hairs about avoiding vs. evading taxes, or generally pontificating about fiduciary duty, without understanding it.