Institution of Neilah

We know who instituted the various tefillos. However, on Yom Kippur we have the once-a-year tefilla of neilah. Who instituted that?

The Chassam Sofer calculates and concludes that Moshe’s 514th tefilla (of his famous 515 tefillos) was mincha of Yom Kippur. Then Moshe arose and instituted the tefilla of neilah. That was his 515th tefilla, the zenith, the special tefilla to finally break through. This is why it says ואתחנן אל ה' בעת ההיא, I implored Hashem at that time, as it was at a specific, special time.