Gittin 18A

ואותביה בכיסתיה ⁠– דאי מפייסה תיפייס, מאי?

and puts it in his pocket without giving it to her, as he thought that if she appeases [mippayyesa] him he will be appeased, what is the halakha when he then does give it to her? Since the date on the document is incorrect, did the rabbis institute an ordinance that such a bill of divorce should not be used?

אמר ליה: לא מקדים אינש פורענותא לנפשיה.

Rava said to him: A person does not hasten a calamity on himself and will not ordinarily prepare a bill of divorce in advance. Rather, he will wait until he is ready to divorce his wife. Since this scenario is unlikely, the rabbis did not see a need to institute an ordinance pertaining to it.

אמר ליה רבינא לרב אשי: גיטין הבאים ממדינת הים, דמיכתבי בניסן ולא מטו עד תשרי ⁠– מה הועילו חכמים בתקנתם? אמר ליה: הנהו, קלא אית להו.

Ravina said to Rav Ashi: When there are bills of divorce that come from a country overseas which are written, For example: in the month of Nisan, and they do not reach the woman until the month of Tishrei, what did the rabbis accomplish with their ordinance to date the bill of divorce? All of the concerns about an undated bill of divorce still apply. He said to him: Concerning these bills of divorce from overseas, it is public knowledge that they do not take effect from the date on which they were written. Therefore, if there is a conflict over produce the husband has sold, the woman must bring witnesses to testify as to when she received her bill of divorce.

איתמר: מאימתי מונין לגט? רב אמר: משעת נתינה, ושמואל אמר: משעת כתיבה.

§ The rabbis decreed that it is prohibited for a woman to remarry within 3 months of her divorce or her becoming a widow, in order to prevent a situation of doubt concerning the paternity of a child. It was stated: From when does one begin counting the 3 months with regard to a bill of divorce? Rav says: From the time of the giving of the bill of divorce, and Shmuel says: From the time of the writing of the bill of divorce.