Reference for Gittin 58:15
וליחוש שמא פייס מי לא תנן מעכשיו אם לא באתי מכאן ועד יב"ח ומת בתוך יב"ח הרי זה גט
A certain man sent a Get to his wife, telling the bearer not to give it to her till thirty days had passed. Before the thirty days had passed, the man found he could not carry out the commission. He therefore consulted Raba. Said Raba: Why is a bearer who falls ill [allowed to appoint another bearer]? Because he is prevented by circumstances [from carrying out his commission]. This man also is prevented by circumstances [from carrying out his commission]. So he said to the man: Transmit your commission to us, so that after thirty days we can appoint a bearer who will give the Get to the wife. Said the Rabbis to Raba: But he is not [at this moment] commissioned to effect the divorce? — He replied: Since he can divorce her after thirty days, he is practically [now] an agent commissioned to divorce her. They rejoined: Do we not take account of the chance that the husband may have made friends with her [within the thirty days]? Have we not learnt: '[If a man says, This is a Get] from now onward if I do not come within twelve months, if he dies within the twelve months, it is a Get,'<span class="x" onmousemove="('comment',' Infra 76a. ');"><sup>14</sup></span>