Rif Gittin 5a {Gittin 11b; Yevamot 118b; Gittin 12a - 13a}

5a

{Gittin 11b}

וא"ת משנתינו
כל האומר תנו כאומר זכו דמי
שמעינן מינה שהתופס לבעל חוב במקום שאינו חב לאחרים קנה:

And if you say: what about our Mishna {which seems to suggest that he does acquire}?
{The answer is:} Whoever says "give" is as if he said "acquire on behalf of."
We derive from this that if one seizes for a creditor in a situation when it is not a loss for others, he acquires.

וחכמים אומרים בגיטי נשים אבל לא בשחרורי עבדים לפי שזכין לו לאדם שלא בפניו:
והני מילי לחזרה דלא מצי רביה למיהדר ביה אבל עבדא לא נפיק לחירות עד דמטי גיטא לידיה
דתנן האומר תנו גט זה לאשתי ושטר שחרור זה לעבדי ומת לא יתנו לאחר מיתה דאין גט לאחר מיתה
ושמעת מינה דלחזרה הוא דזכין לו לעבד אבל מיפק לחירות לא נפיק עד דמטי גיטא לידיה
ואשכחן זכייה כה"ג כדאמרי' לקמן הולך מנה לפלוני שאני חייב לו אמר רב חייב באחריותו ואם בא לחזור אינו חוזר:

"THE SAGES, HOWEVER, SAY THAT HE MAY COUNTERMAND IN THE CASE OF THE GET BUT NOT IN THAT OF THE WRIT OF EMANCIPATION, ON THE PRINCIPLE THAT A BENEFIT MAY BE CONFERRED ON A MAN IN HIS ABSENCE...":
And these words are in terms of retraction, such that his master is not able to retract from it. But still, the slave does not go out to freedom until the get reaches his hand. For they learnt {in a Mishna}: If one says "give this get to my wife and this bill of manumission to my slave" and he dies, they do not give it after death, for there is no get after death. And you can derive from this that it is in terms of retraction that we acquire on behalf of the slave, but going out to freedom, he does not go out, until the get reaches his hand.
And we find this type of acquiring benefit as we say later on {in Gittin 14a}: "Take this maneh to Ploni, which I owe him" -- Rav said: He {the sender} is {still} responsible for it, and {yet} if he wishes to retract {the sending of the maneh} he may not retract.

גרסינן בפרק האשה שהלכה היא ובעלה למדה"י שלום בינו לבינה
בעא מיניה רבא מרב נחמן המזכה גט לאשתו במקום יבם מהו
כיון דסניא ליה זכות הוא לה וזכין לאדם שלא בפניו
או דילמא כיון דזימנין דרחמא ליה ליבמה חוב הוא לה ואין חבין לאדם שלא בפניו
אמר ליה תניתוה וחוששין לדבריה וחולצת ולא מתיבמת
אמר ליה רבינא לרבא המזכה גט לאשתו במקום קטטה מהו
כיון דאית לה קטטה בהדיה זכות הוא לה או דילמא ניחא דגופה עדיף לה
תא שמע דאמר ריש לקיש טב למיתב טן דו מלמיתב ארמלו:

We learn in perek haIsha shehalcha hi uvaalah limdinat hayam, shalom beino leveinah {Yevamot 118b, also here in Rif}:

Rava asked of Rav Nachman: If one gave over a get {to an agent on behalf of his wife, but he appointed this agent rather than she} in case of a levir {such that it is to her benefit, so that she need not undergo yibbum or chalitza}, what {is the law}?
Since she hates him {the levir}, it is a benefit to her, and we accrue benefit on behalf of a person even when not before them? Or perhaps since there are times that she loves her levir, it is a disadvantage, and we do not impose disadvantages on behalf when not in front of them?
He said to him: We have learned it: "And we worry for her words and so she performs chalitza but not yibbum" {thus, in some cases she hates him and in some she loves him, so it is a chov}
Ravina said to Rava: If one gave over a get {to an agent on behalf of his wife, but he appointed this agent rather than she} in case of discord {between them}, what {is the law}? Since there is discord with him, it is a benefit to her? Or perhaps, an easier physical state {for she is being supported, or is gratifying bodily desires} is better for her?
Come and hear {a proof}: For Rabbi Shimon ben Lakish said: It is better to live as two {alternatively, in grief} than to live in widowhood.

{Gittin 12a}

שאם רצה שלא לזון את עבדו רשאי.
שמעת מינה יכול הרב לומר לעבד עשה עמי ואיני זנך
ומסקנא ת"ש הקוטע יד עבדו של חברו נותן שבתו ורפואתו לרבו ואותו העבד ניזון מן הצדקה
שמעת מינה יכול לומר לעבד עשה עמי ואיני זנך ש"מ:

"FOR IF HE CHOOSES NOT TO MAINTAIN HIS SLAVE HE IS PERMITTED":
{A supposition:} We derive from this that the master is permitted to say to the slave "work for me yet I will not support you."
{Gittin 12b}
And the conclusion: Come and hear: He who cuts off the hand of his friend's slave gives the loss of time {in which the slave cannot work} and the cost of his medical attendance to the master, and the slave is supported from charity.
We derive from this that he is able to say to a slave "work for me and {yet} I will not support you." We so derive.

רפואתו דרבו היא, דידיה היא דבעי איתסויי בה.
לא צריכא דאמדוהו לחמשא יומי ועבדו ליה סמא חריפא ואיתסי בתלתא יומי
מהו דתימא צערא דידיה הוא
קמ"ל דההוא טופיאנא לרביה הוא

The cost of his medical attendance goes to his master? Surely it should go to him, for he needs to be cured with it?
No, it is necessary, for where they estimate that he will take five days and by applying a painful remedy he was cured in three days. I would have thought that the pain is his {such that since he underwent the pain, he gets to keep the extra money that would have been spent on a doctor for those extra two days}. Therefore it informs us that the surplus belongs to the master.

{Gitttin 13a}
Mishna:

האומר תנו גט זה לאשתי ושטר שחרור זה לעבדי ומת לא יתנו לאחר מיתה
תנו מנה לפלוני ומת יתנו לאחר מיתה

IF A MAN SAYS, GIVE THIS GET TO MY WIFE, THIS DEED OF EMANCIPATION TO MY SLAVE, AND DIES [BEFORE THEY ARE GIVEN], THEY ARE NOT TO BE GIVEN AFTER HIS DEATH. [IF HE SAID], GIVE A MANEH TO SO-AND-SO AND DIED, THE MONEY SHOULD BE GIVEN AFTER HIS DEATH.

Gemara:

מתני' בשכיב מרע והיינו טעמא דמתני' דדברי ש"מ

The Mishna was addressing the case of one deathly ill. And this is the reason of the Mishna -- that the words of a person deathly ill