Gittin 25B

ומיחל ושותה מיד, דברי רבי מאיר. רבי יהודה ורבי יוסי ורבי שמעון אוסרין.

And he deconsecrates the second tithe that he will separate in the future, transferring its sanctity to money, and he may drink the wine immediately, relying on the separation that he will perform later, which will clarify retroactively which log he designated for the tithes and for teruma. This is the statement of R' Meir. However, R' Yehuda and R' Yosei and R' Shimon prohibit this practice, as they hold that in this case there is no retroactive clarification. It is therefore evident that according to R' Yehuda, there is no retroactive clarification where one makes the clarification dependent on his own decision.

תולה בדעת אחרים אית ליה ברירה ⁠– דתנן: מה היא באותן הימים?

By contrast, in a case where one makes the outcome dependent on the decision of others, R' Yehuda accepts the principle of retroactive clarification, as we learned in a Mishnah (73a): In a case where an ill husband says to his wife: This is your bill of divorce from now if I die due to this illness, if he dies, the bill of divorce takes effect from the time of his statement. The Mishnah asks: What is the halakhic status of the wife in those days between when the bill of divorce was given but before the husband died?

רבי יהודה אומר: הרי היא כאשת איש לכל דבריה, ולכי מיית הוי גיטא.

R' Yehuda says: She is like a married woman with regard to all of her matters, and she remains forbidden to other men; and when he will die, it is a bill of divorce. Death is equivalent to a matter that is dependent on the decision of others. Since R' Yehuda agrees that the bill of divorce takes effect retroactively, as it cannot take effect after the death of the husband, he evidently holds that there is retroactive clarification where one makes the clarification dependent on the decision of others.