Bava Basra 130b: You cannot derive halacha from a story (because you may be mistaken about the reason for the rav’s decision in that story), unless it was your personal story that you presented to the rav, and the rav issued an actual ruling based only on the facts supplied to him.
בבא בתרא קל ע”ב תנו רבנן: אין למדין הלכה לא מפי למוד ולא מפי מעשה ־ עד שיאמרו לו הלכה למעשה.
רשב”ם: ולא מפי מעשה־ אם יראה רבו עושה מעשה אל יקבע הלכה בכך דשמא טעה בטעם של פסק דין של אותו המעשה… עד שיאמרו לו הלכה למעשה־ דכיון ששאל ע״י מעשה ואינן יודעין בדבר אלא מה שהוא אומר להם אין לומר טעם חזו ביה דלא ידע.
צוואת רבי יהודה החסיד אות נא: לא יקרא איש מזרעו את בנו יהודה ולא שמואל.
Rabbi Yehuda Hechassid writes in his tzavaah that his descendents must not name a child Yehuda or Shmuel. Once, at a gathering of rabbis, they began to discuss whether it is obligatory to keep Rabbi Yehuda Hechassid’s tzavaah. The Maharsha stood up and said, “I am descended from Rabbi Yehuda Hechassid, yet my name is Shmuel, and my father’s name is Yehuda. Rabbi Yehuda Hechassid only meant to ban those names for his immediate family, to avoid fights over who should have the privilege of naming a child after him or after his father Shmuel.” This shows that even one who is careful to keep everything written in the tzavaah (or in Sefer Chassidim) must know the context in which it was said, in order to know when to apply it.
Source: Rabbi Reisman, tape on YD 184:11
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