Yevamot 93B

אלא לאו, כי האי גוונא. אמר ליה: והא אקריון בחלמא ״קנה רצוץ״, מאי לאו, הכי קאמרי לי: ״הנה בטחת לך על משענת הקנה הרצוץ הזה״?

Rather, is it not referring to a case like this, of one who tithed an entity that was not yet in the world, in honor of Shabbat? R' Yannai said to R' Ḥiyya: But they read before me in a dream these two words: Bruised reed. What, is it not the case that they said to me as follows: “Behold you trust upon the staff of this bruised reed” (II Kings 18:21)? In other words, you rely on an unsubstantiated idea.

לא, הכי קאמרי לך: ״קנה רצוץ לא ישבור ופשתה כהה לא יכבנה״.

R' Ḥiyya said to him: No; The dream referred to a different verse, one that deals with the Messiah, as they said to you as follows: “A bruised reed he should not break and the dimly burning wick he should not quench; according to truth he should bring forth justice” (Isaiah 42:3). In other words, R' Yannai acted correctly, in accordance with the ways of truth. This exchange shows that both R' Ḥiyya and R' Yannai agree that an entity not in the world can be acquired.

רבי ⁠— דתניא: ״לא תסגיר עבד אל אדוניו״, רבי אומר: בלוקח עבד על מנת לשחררו הכתוב מדבר. היכי דמי? אמר רב נחמן בר יצחק: דכתב ליה לכשאקחך ⁠— הרי עצמך קנוי לך מעכשיו.

With regard to R' Yehuda HaNasi, his opinion is as it is taught in a baraita: The verse states: “You should not deliver a slave to his master” (Deuteronomy 23:16). R' Yehuda HaNasi says: The verse is speaking of one who buys a slave on the condition to free him. This owner may not keep his acquisition as a slave. The Talmud clarifies: What are the circumstances? Rav Naḥman bar Yitzḥak said: It is referring to a case where one wrote to a slave in the document of acquisition: When I acquire you as a slave, you are acquired by yourself from now. In this case, the buyer transfers ownership of an entity not yet in the world, as the slave did not yet belong to him.