Gittin 3:8-4:1

Gittin 3:8

If a person puts produce aside to later designate terumah and maaser from it, or if he puts money aside to later designate second tithe from it, he may do so under the assumption that it still exists. If the produce or money was lost, he must act according to the assumption that it was lost within the preceding 24 hours; this is the opinion of Rabbi Elazar ben Shamua. Rabbi Yehuda says that wine is examined at three junctures: when the east wind blows after Succos, when the blooms fall off the flowers and when moisture enters unripe grapes.

Gittin 4:1

Let’s say that a man sent his wife a get and then he caught up to the one delivering it, or he sent another person to catch the one delivering it, and they inform the messenger that the get is canceled. In such a case, the get is effectively canceled. If the man or his agent reached the wife before the messenger and told her that the get is canceled, then it is canceled. Once the get has reached her hand, he can no longer cancel it.