I might be late to this. But in Material Design website it does have a sample of it.
In most cases I think text only or icon only are sufficient to describe what it does. I came across a scenario where the button text describes the item that user is selecting and button icon describes what happens when the button is clicked. It seems more 'instructive' to me. But I may be wrong.
The following examples are from Material Design website.
Use icons that clearly communicate their meaning.
Don’t vertically align an icon and text in the center of a contained button.