Parashas Eikev · Passuk 9:25
When I lay prostrate before GOD those forty days and forty nights,athose forty days and forty nights Lit. “the forty days and forty nights that I lay prostrate.” because GOD was determined to destroy you,
Torah Temimah points to Berachos 34a.
TT lemma: את ארבעים היום וגו'.
English: Our Rabbis taught: A student once served as prayer leader before R’ Eliezer and was excessively long. His students said: How long-winded he is! He replied: Is he more long-winded than Moshe Rabbeinu, of whom it is written, “I threw myself down before Hashem for forty days and forty nights”? Conversely, when a student was excessively brief, R’ Eliezer said: Is he briefer than Moshe, who said, “Please heal her, please”?
Custom (length of prayer — Moshe as measure)
Neither extreme length nor extreme brevity of prayer is beyond the precedent of Moshe; both have their place.