Basis on conversion of home to rental when sale >FMV

I have found a bunch of links like the following that explain that the basis at sale when conversion FMV < initial purchase price is the purchase price.

https://www.kahnlitwin.com/blogs/tax-blog/converting-a-personal-residence-to-a-rental-property

https://www.marketwatch.com/story/want-to-convert-your-home-into-a-rental-property-here-are-the-tax-...

https://ecohencpas.com/consider-taxes-before-converting-your-home-to-a-rental-property/


Several other articles explain that IRS will only allow the FMV at conversion as the basis. 

I havent found the IRS clause/para for the special basis treatment. 

Which rule is correct?