Bechoros 44b:
אמר רבי אבא בריה דרבי חייא בר אבא משתינין מים בפני רבים ואין שותין מים בפני רבים ותניא נמי הכי משתינין מים בפני רבים ואין שותין מים בפני רבים ומעשה באחד שביקש להשתין מים ולא השתין ונמצא כריסו צבה. שמואל איצטריך ליה בשבתא דרגלא נגדו ליה גלימא אתא לקמיה דאבוה א”ל אתן לך ד’ מאה זוזי וזיל אהדר עובדא את דאפשר לך דלא אפשר ליה ליסתכן…
What does “Ahadar Uvda” mean?
Rashi explains:
אהדר עובדא, דרוש שאסור להמתין מלהטיל מים עד שיהא לו צניעות.
If retraction is just oral, such a large sum of money seems excessive as a reward for doing his clear duty. Rather, it appears the retraction referred to here means to do Teshuvas Hamishkal: Teach again and urinate without a mechitza. Perform a Ma’aseh Rav to counteract the faulty one.
Soncino agrees with me, for what that’s worth:
R. Abba b. R. Hiyya b. Abba reported in the name of R. Johanan: It is permitted to urinate in public, whereas it is not permitted to drink water in public. So indeed it has been taught: It is permitted to urinate in public, whereas it is not permitted to drink water in public. And it once happened that someone wanted to urinate and forewent it, and it was found that his belly was swollen.
Samuel needed to urinate on a Sabbath preceding a Festival. He spread his cloak [as a screen between his audience and himself]. He came before his father [and reported this to him]. He [the latter] then said to him: ‘I will give you four hundred zuz to retract* this ruling, for you were able to spread a cloak, but one who is not able to do so, shall he delay and expose himself to the danger?’
* To urinate in their presence and thus proclaim that it was not necessary to exercise privacy when requiring to urinate.
Maybe that’s why the sum is exactly 400 Zuz (the fine paid for shaming a Jew).