SpaceX on Jan 13, 2021 did three static fires in one day.
Elon Musk tweeted:
All three static fires completed & no RUDs!
And that was in response to this tweet of his own:
Today at SpaceX is about practicing Starship engine starts. Ship is held down by massive pins while engines are fired. Two starts completed, about to try a third.
This is a 400,000 lb thrust engine, and they fired three of them, three times in the same day on a prototype launch vehicle.
Has there ever been anything even close? In terms of three firings in one day?
Smaller engines like XCOR have been fired multiple times in one day, but not even within 3 orders of magnitude of thrust level, nor 3 big boys at one time.