I remember seeing an early authoritative source (Rishonim, maybe a Tosfos?) that noted which numbers are always (technically not always) used by the Rabbis to indicate exaggeration in stories (60, 300, etc.), but I don't remember where I saw it. So I pose the question:
What is the earliest source you can find that identifies certain numbers as being used by Chazal as hyperbole (not just in a situation or two, but systematically), and which numbers are they?