Pesachim 104B

ולית הלכתא כוותיה.

However, the Talmud states: And the halakha is not in accordance with that opinion. Instead, the halakha is in accordance with the opinion of Shmuel.

עולא איקלע לפומבדיתא, אמר ליה רב יהודה לרב יצחק בריה: זיל אמטי ליה כלכלה דפירי, וחזי היכי אבדיל. לא אזל, שדר ליה לאביי. כי אתא אביי, אמר ליה: היכי אמר? אמר ליה: ״ברוך המבדיל בין קודש לחול״ אמר, ותו לא.

The Talmud relates: Ulla happened to come to Pumbedita. Rav Yehuda said to his son, Rav Yitzḥak: Go and bring him a basket of fruit as a gift, and while you are there, observe how he recites havdala. Rav Yitzḥak himself did not go. In his place, he sent to him Abaye, who was a young student at the time. When Abaye came back, Rav Yitzḥak said to him: How did Ulla recite the blessing of havdala? Abaye said to him that Ulla said: Blessed is He Who distinguishes between sacred and profane, but he did not say anything further.

אתא לקמיה דאבוה, אמר ליה: היכי אמר? אמר ליה: אנא לא אזלי, אנא שדריתיה לאביי, ואמר לי ״המבדיל בין קודש לחול״. אמר ליה: רברבנותיה דמר, וסררותיה דמר, גרמא ליה למר דלא תימא שמעתיה מפומיה.

Rav Yitzḥak came before his father, Rav Yehuda, who said to him: How did Ulla recite havdala? He said to him: I myself did not go. Instead, I sent Abaye, who said to me that Ulla recited: Who distinguishes between sacred and profane. Rav Yehuda grew angry and said to him: The Master’s haughtiness and the Master’s pride caused the Master to act in a way that ensured that the halakha will not be said in his name. In other words, had you gone yourself, this halakha would have been attributed to you, but due to your haughtiness and pride, it will be transmitted in the name of Abaye.

מיתיבי: כל הברכות כולן פותח בברוך וחותם בהן בברוך, חוץ מברכת מצות וברכת הפירות וברכה הסמוכה לחבירתה וברכה אחרונה שבקרית שמע,

The Talmud raises an objection to Ulla’s practice from a baraita: With regard to all blessings, one begins their recitation with: Blessed, and concludes reciting them with: Blessed, except for blessings over mitzvot, blessings over fruit, a blessing that is juxtaposed to another blessing in the order of prayer, e.g., during the Amida prayer, and the final blessing after Shema.