… is from page 144 of Bruce Caldwell’s and Hansjoerg Klausinger’s 2022 Hayek: A Life, 1899-1950 [reference deleted; link added]:
During the [first world] war [Ludwig von] Mises had gained a reputation for his financial acumen, yet in the face of the the Austrian hyperinflation it was not necessary for him to turn to the subtleties of his own monetary writings, as the simple insights from the quantity theory of money sufficed for suggesting a solution. This is highlighted by the “apocryphal story” recalled [by Hayek] in an interview, according to which “Mises was asked during that inflation how to stop it. And he said, ‘Meet me at 12 o’clock at this building.’ And it turned out at 12 midnight they met him at the printing office, where they were printing the money. And they said, ‘How can we stop this inflation?’ And he said, ‘Hear that noise? Turn it off.'”