Gittin 45A

ורב ענן ⁠– ברייתא לא שמיע ליה;

The Talmud says: And as for Rav Anan, who could not determine in which case the money of the sale is returned, the baraita was not known to him, so he was not able to use it in order to resolve his dilemma.

ואי מדשמואל ⁠– ממאי דאינה מכורה ומעות חוזרין, דילמא אינה מכורה ומעות מתנה נינהו ⁠– מידי דהוה אמקדש את אחותו, דאיתמר: המקדש את אחותו, רב אמר: מעות ⁠– חוזרין, ושמואל אמר: מעות מתנה.

And if Rav Anan would attempt to resolve his dilemma from the statement of Shmuel, who said that the sale does not take effect at all, this should mean that the money used in the sale is returned, and it is possible to say: From where can you assume that it is not sold, and therefore the money is returned? Perhaps it is not sold and the money is considered to be a gift, just as it is according to the opinion of Shmuel in the case of one who betroths his sister. As it was stated with regard to one who betroths his sister, Rav said: The money he gave for the betrothal is returned, since the betrothal does not take effect; and Shmuel said: This money is a gift, meaning that he wished to give a gift to his sister and he did so in this manner. Therefore, Rav Anan remained uncertain as to when Shmuel required the money to be returned.

אמר ליה אביי לרב יוסף: מאי חזית דקנסינן ללוקח? נקנסיה למוכר! אמר ליה: לאו עכברא גנב אלא חורא גנב. אמר ליה: אי לאו עכברא, חורא מנא ליה?

With regard to the halakha that if one sells his slave to a Jew outside of Eretz Yisrael it is the purchaser who loses his money, Abaye said to Rav Yosef: What did you see to cause you to say that we apply the penalty to the purchaser, in that he is required to emancipate the slave and loses his money; we should apply the penalty to the seller, and he should be required to return the money. Rav Yosef answered Abaye with a parable and said to him: It is not the mouse that steals, but the hole that steals. In other words, a mouse cannot steal anything unless he has a hole for hiding the stolen items. Here too, the slave would not have been sold without the help of the purchaser. The Talmud questions this logic: But if not for the mouse, from where would the hole have the stolen item; since they both contribute to the prohibited act, each of them is deserving of being penalized.