I think the easiest way to explain why it can't be done is this:
Before the loan this person had $50k in pre-tax IRA and $50k in pre-tax 401(k) money. A total $100k he will need to pay taxes at distribution.
They take a loan and have no taxable income.
The use the $50k in IRA money to repay the loan.
So now they have $0 in pre-tax IRA and only $50k in pre-tax 401(k) yet they received $50k in cash without paying any taxes. Clever but I don't think it works for the reason Tom says. A rollover is a rollover. They would have to take an IRA distribution and then pay the loan. A rollover can't be both a loan payment and a rollover by definition. I think that is why you can't find a cite. it is embedded in the very definition of the words.
I once worked for a very wealthy man whose wife told him on their wedding day (back in the 1940s) that he could have a divorce any time he thought he could afford it.
They stayed married until he died some 45 years later.
I know my parents always told me that they were "divorce-proof," since they had an agreement that whoever ASKED for the divorce had to take 100% custody of us kids!