Beitzah 37B

דלא כרבי דוסא, דתניא: רבי דוסא אומר, ואמרי לה: אבא שאול אומר, הלוקח בהמה מחברו מערב יום טוב, אף על פי שלא מסרה לו אלא ביום טוב ⁠— הרי היא כרגלי הלוקח. והמוסר בהמה לרועה, אף על פי שלא מסרה לו אלא ביום טוב ⁠— הרי היא כרגלי הרועה.

is not in accordance with the opinion of R' Dosa. As it is taught in a baraita: R' Dosa says, and some say Abba Shaul says: One who purchases an animal from another on the eve of a Festival, even if he did not deliver it to him until the Festival itself, it is as the feet of the purchaser. And one who delivers his animal to a shepherd, even if he did not deliver it to him until the Festival itself, it is as the feet of the shepherd. The Mishnah, on the other hand, teaches that an animal delivered to a shepherd remains as the feet of the owner, therefore apparently contradicting R' Dosa.

אפילו תימא רבי דוסא, ולא קשיא: כאן ברועה אחד, כאן בשני רועים. דיקא נמי דקתני: לבנו או לרועה, שמע מינה.

The Talmud rejects the assertion that this is a contradiction. You can even say that the Mishnah is in accordance with R' Dosa, and it is not difficult. Here, in the baraita, it is referring to a town that has only one shepherd. In that case the owner knows with certainty beforehand that he will be delivering his animal to this shepherd over the course of the Festival, and therefore the animal’s place of rest is established as being identical to that of the shepherd. There, however, the Mishnah is referring to a town where there are two shepherds. Since the issue of which of them will receive this animal is undetermined when the Festival begins, the animal remains as the feet of its owner. The Talmud strengthens this assertion that the Mishnah is dealing with a case where there are two shepherds: The language of the Mishnah is also precise in accordance with this interpretation, as it teaches: To his son or to a shepherd, suggesting that initially he did not know to whom he would give the animal. The Talmud concludes: Indeed, learn from this that this is so.