That's exactly what I said when Trump was threatened with impeachment if he fired Jeff Sessions.
As far as links to stories about threats to impeach Trump over possibly firing Sessions, I found a ton of stories about the whole kerfuffle, but my weak eyes can't make out the script at most of those websites. Sorry 'bout that.
The whole Republicans Will Impeach Trump idea developed a life of its own.
IMO it was nothing more than a rationale cooked up by a crowd that talked themselves into the idea that Sessions isn’t doing his job. They would have no possible way of knowing that since he doesn’t have to give briefings to the nosy public, but that doesn’t stop them from announcing their opinions as fact.
The one man who does know if Sessions is doing his job is Trump. And if he decided to fire Sessions there’s not a damned thing that Congress could do about it. They simply cannot interfere with a president firing his executive branch staff, AG included. An attempt by Congress to impeach a president for firing one of his cabinet officers would be nothing short of a coup. And Congress knows it.