Rif Gittin 8b {Yerushalmi Gittin 21b; Bavli Gittin 18a - b}

8b

איכא מ"ד הלכתא כר' יוחנן ואיכא מאן דאמר הלכתא כר"ש בן לקיש דאמר משעת כתיבה כדקי"ל לענין ג' חדשים
והא לאו מילתא היא דהתם לענין מאימתי מונין לגט ביחוד תליא מילתא וכיון דאינו מתיחד עמה משעת כתיבה מונין משעת כתיבה
אבל הכא לענין פירי בפרקונה תליא מילתא כדאמרי' תיקנו פרקונה תחת פירות
וקי"ל דלא פקע פרקונה מיניה עד דמטי גיטא לידה הלכך כל כמה דמחייב בפרקונה אית ליה פירי ושמעת מינה דהלכתא כרבי יוחנן דאמר יש לבעל פירות עד שעת נתינה:

There is one who says that the halacha is like Rabbi Yochanan, and there is one who says that the halacha is like Rabbi Shimon ben Lakish, who said that it is from the time of writing, as we establish in terms of the three months {before remarriage}. And this is no evidence, for there, it is in terms of from when we count for a get, and in seclusion together the matter depends, and since he does not seclude himself with her from the time of writing. But here, in terms of increase, the matter is dependent upon her redemption {that he gets this in exchange for his obligation to redeem her if she is captured}, as we said, "they instituted her redemption in exchange for the increase." And we establish that her redemption does not leave her until the get reaches her hand. Therefore, so long as he is obligated in her redemption, he has the increase.
And we derive from this that the halacha is like Rabbi Yochanan who said that the husband gets the increase until the time of the giving.

Yerushalmi {Yer Gittin 21b}:

ירושלמי
מעשה באחד שהיה נשוי בת אחותו וזינתה עד שהיא אשתו
עמד וגרשה והקדים זמן הגט אמר מוטב שתידון בפנויה ולא כאשת איש

There was an incident in which someone married his sister's daughter and she committed adultery when she was his wife. He arose and divorced her, and set the date of the get earlier. He said "it is better that she be judged as an unmarried woman and not as a man's wife."

{Gittin 18a}

איתמר מאימתי מונין לגט
רב אמר משעת נתינה ושמואל אמר משעת כתיבה
תניא כותיה דשמואל המשליש גט לאשתו ואמר אל תתנו לה אלא לאחר שלשה חדשים משנתנו לה מותרת לינשא מיד ולגט ישן אין חוששין שהרי לא נתייחד עמה
וכן הילכתא

It was stated {by Amoraim}:
From when do we count {three month from the time of divorce to determine whether the woman is pregnant from the previous spouse}?
Rav said: From the time of giving {of the get}. And Shmuel said: From the time of the writing.
There is a brayta in accordance with Shmuel: If a person entrusts his get to a third party, and states "do not give it to her until after three months," once he gives it to her, she is permitted to marry immediately. And we are not worried about an "old" get, for behold, he did not seclude himself with her.
And so is the halacha.

{Note: In the gemara, there is also a brayta in accordance with Rav, so it is not merely the brayta that leads to this conclusion. But the gemara states:
Rav Kahana, Rav Papi and Rav Ashi acted on the principle that the Get is valid from the time of writing; Rav Pappa and Rav Huna the son of Rav Joshua that it is valid from the time of delivery. The law is that it is valid from the time of writing.
And Rif is endorsing the conclusion of the gemara.}

אמר שמואל כתובה כמעשה בית דין דמיא
מה מעשה ב"ד נכתבין ביום ונחתמין בלילה אף כתובה נכתבת ביום ונחתמת בלילה

כתובתה דחייא בר רב אכתיב ביממא ואיחתים בליליא
הוה רב התם ולא אמר להו ולא מידי
לימא כשמואל ס"ל לא עסוקין באותו ענין הוו
ותניא אמר רבי אלעזר בר צדוק לא שנו אלא שאין עסוקין באותו ענין אבל עסוקין באותו ענין כשר:

Shmuel said: The ketuba is like the act of bet din. {a deed drawn up in bet din}
Just as an "act of bet din" may be written during the day and signed at night, so too the ketuba may be written during the day and signed at night.

The ketuba of Chiyya bar Rav was written during the day and signed at night. Rav was present and did not say a single thing {=he did not object}. Let us say that he held like Shmuel. No, they were still dealing in the same topic {and so they could continue into the night}.
And a brayta {showing this position}: Rabbi Eleazar bar Tzaddok said: They only learned this where they were not engaged in that topic, but if they were engaged in that topic, it is valid.

{Gittin 18b}

איתמר אמר לעשרה כולכם כתבו גט לאשתי
אמר ר' יוחנן שנים משום עדים וכולן משום תנאי
ור"ש בן לקיש אמר כולן משום עדים
מאי בינייהו דחתים בי תרי מינייהו ביומיה והנך מכאן ועד י' ימים
לר' יוחנן דאמר משום תנאי כשר
ולרבי שמעון בן לקיש דאמר משום עדים פסול

אי נמי כגון שנמצא אחד מהן קרוב או פסול
מאן דאמר משום תנאי כשר

It was stated {by Amoraim}:
If he said to ten {people}: All of you, write a get to my wife.
Rabbi Yochanan said: Two of them are witnesses and all of them are because of a condition {he made}.
And Rabbi Shimon ben Lakish said: All of them are witnesses.
What is the {practical} distinction between them? Where two of them signed on the same say, and the other ones from then until 10 days later.
According to Rabbi Yochanan who said that it is because of a condition, it is valid.
And according to Rabbi Shimon ben Lakish who said that they {all} have the status of witnesses, it is invalid.

Alternatively, when one of them is found to be a relative or someone who is invalid. The one who said that it is because of the condition, it is valid.