Marx, rabbi soloveitchik had to say it; for everyone else, it was self understood.
One source for the above that comes to mind is the netzviv’s famous line about how even if the rambam would testify after techias hamaysim that he didn’t mean what various achronim write as pshat in his words, it wouldn’t detract from the truth of those achronim’s explanations, because once the rambam was written, it became a part of the continuum of klal yisroel’s Torah transmission and he is not the baal habayis on it.
I’ve seen that netzviv quoted in several places… I’ll try to find one for you bl”n