You have to go pretty far back, it was in the Visual C++ 6.0 EULA, for instance (for lack of a better link):

https://proact.eu/wp-content/uploads/2020/07/Visual-Basic-En...

It wasn't a blanket prohibition, but a restriction on some parts of the documentation and redistributable components. Definitely was weird to see that in the EULA for a toolchain. This was removed later on, though I forget if it's because they changed their mind or removed the components.