Gemara

7a (Rav Papi): One blesses '... Leva'er (to get rid of) Chametz';

(Rav Papa): He blesses 'Al Bi'ur Chametz'.

All agree that Leva'er connotes the future. Rav Papi holds that "Al" connotes the past. Rav Papa holds that it connotes the future.

Question (Beraisa): One who circumcises blesses '...v'Tzivanu Al ha'Milah.'

Answer: There, one cannot bless 'Lamul', for this implies that he himself must circumcise. This is not so!

Question: When a father circumcises his son, he should bless 'Lamul'!

Answer: Indeed, Rav Papi says so!

Question (Beraisa): [One who slaughters blesses] '... Al ha'Shechitah'!

Answer: He cannot bless 'Lishchot', which implies that he himself must slaughter.

Question: One who slaughters his Korban Pesach should bless 'Lishchot'!

Answer: Indeed, Rav Papi says so!

Question (Beraisa): One blesses '... Al Netilas Lulav'.

Answer: There the past tense is proper, for he already fulfilled the Mitzvah once he picked them up!

98b (Mishnah): If a group sent a member to slaughter their Korban Pesach... all eat from the animal he slaughtered.

Kidushin 41b - Question: What is the source that a Shali'ach can slaughter Kodshim?

Answer (R. Yehoshua ben Korchah) Question: Why does it say "all of Yisrael will slaughter [the Pesach]"? Only one person slaughters (each Korban)!

Answer: This teaches that we attribute a Shali'ach's actions to the Meshale'ach (who appointed him).

Nedarim 72b (Beraisa - R. Yonason): In the entire Torah, one's Shali'ach is like himself.

Bechoros 50a: Rav Ashi sent 17 Zuz to Rav Acha brei d'Ravina (a Kohen) for Pidyon ha'Ben.

Chulin 87a (Beraisa): "V'Shafach... v'Chisahu" - the one who spills the blood (slaughters) must cover it;

"Daber El Bnei Yisrael" obligates everyone.

Rishonim

Rosh (Chulin 6:8): Even if Reuven asked Shimon to circumcise Reuven's son, Shimon did not acquire the Mitzvah to obligate someone else who does it first. This is unlike Kisuy ha'Dam. The Torah said that the one who slaughters [a bird or Chayah], he covers. However, if Reuven does not want to circumcise his son, all of Yisr ael are obligated to do so.

Ran (3b DH v'Kashya): Some Mitzvos one must fulfill himself, and he cannot fulfill them through others, e.g. Tefilin, Tzitzis and Sukah. All agree that one must bless on them with a "Lamed" (e.g. Leshev"). This shows that the Mitzvah is incumbent on him. The Gemara challenged the one who says that we bless Leva'er from "Al ha'Milah." This shows that we normally bless Al. It answered that when the father is alive, he must do the Mitzvah. Therefore, [another - Hagahos Alfas Yashan 2] cannot bless Lamul, which connotes that he must circumcise, which is wrong. Other Mitzvos one can do through others, even if it is incumbent on him, e.g. Bi'ur Chametz and Pidyon ha'Ben. When someone else does such a Mitzvah, all agree that he blesses 'Al'. The Amora'im argue about one who does them himself. If Al connotes also the future, it is better to bless Al, to teach that one can do the Mitzvah through another. One blesses Al Netilas Lulav, even though he must take it himself, for he was already Yotzei once he picked it up; Rav Huna says to bless Al Achilas Maror if he already ate Maror for Karpas. However, why do we bless Lehadlik Ner Chanukah? A Shali'ach can do it! It is because one must pay part of the cost of the oil. One cannot fulfill this through another.

Question (in Rivash 131): Why does the Rambam say to bless 'Al Pidyon ha'Ben' when redeeming his son? The Mitzvah is on the father. We expound that if one was not redeemed, he has a Mitzvah to redeem himself. There is no Mitzvah through a Shali'ach or through Beis Din...

Tosfos Rid (Kidushin 42b DH She'ani): Shelichus does not help for a Mitzvah on the body, e.g. to sit in a Sukah. The Torah commanded his body. How can he be Yotzei through a Shali'ach?! Shelichus works for Gitin, Kidushin, Terumah and [Shechitas] Pesach, for the Meshale'ach divorces, is Mekadesh, gives Terumah from his Peros, and eats Pesach and it is slaughtered for him. Regarding Sukah, Lulav, Tzitzis and all [similar] Mitzvos, the Meshale'ach does not do anything.

Poskim

Shulchan Aruch (YD 28:8): The Shochet covers the blood. If he did not, and another saw, he covers it.

Taz (8): The Tur says that the Mitzvah is on all of Yisrael, just the Shochet is obligated first.

Simlah Chadashah (9): If one who is not a Shochet wants to do the Mitzvah, the Shochet can honorably authorize him to do so occasionally. He may not sell it for money, or make a Shali'ach because he does not want to exert himself.

Tevu'os Shor (14): Do not say that covering is the Shochet's Mitzvah, so he may not give it to another to honor him. We learn from Milah. Very often a Mohel honors another with the Mitzvah. The Rosh compares these Mitzvos. A Kohen has a Mitzvah to offer his own Chatas, but he may give it to another Kohen (Bava Kama 109b). It is a Mitzvah to tithe one's Peros, yet we learn from Terumah that one may make a Shali'ach! The Mitzvah is for the oldest brother to do Yibum, but he may let another brother do Yibum (Yevamos 39a). One who lives in a house must affix a Mezuzah, but he may make a Shali'ach to do so. A Kohen who offered a Minchah is commanded to eat it (Yevamos 40a). This is only due to an extra verse. We say that it is a greater to do a Mitzvah oneself than through a Shali'ach (Kidushin 41a). This is if he does not want to toil. If one honors others with the Mitzvah, this is good for both of them.

Rema (305:10): A father cannot redeem his son through a Shali'ach. Beis Din cannot redeem the son without the father.

Taz (11): The questioner in the Rivash said so, and the Rivash did not mention this. The Rema inferred that the Rivash agreed. This is astounding. In the entire Torah, one's Shali'ach is like himself. What is the source to exclude Pidyon ha'Ben?! Tzedah l'Derech (Parshas Bo) says that if the father died before 30 days, the grandfather or Beis Din can redeem; the Maharal of Prague ruled like this. He is correct. The Ran says that a Shali'ach can do Milah and Pidyon ha'Ben. I say that when the father is alive, he can make a Shali'ach for Pidyon ha'Ben. Anyone may give on behalf of him. He is like the father's Shali'ach, just like one may take Terumah on behalf of another.

Drishah (3 DH Im): The Rivash connotes that the father cannot make a Shali'ach for Pidyon ha'Ben, and Beis Din cannot redeem. Semak holds that even in another city (the son is not there), a Shali'ach can redeem.

Shach (11): In the entire Torah, one's Shali'ach is like himself. The Ran allows redeeming through a Shali'ach. Ma'adanei Melech (Sof 266) and several Gedolei ha'Dor agree, unlike the Rema. Even the Rivash said only that the Torah did not obligate others to be a Shali'ach for the father.

Gra (17): Even one who is not a Shali'ach can redeem. This is no more stringent than Ma'aser Sheni [which anyone can redeem].

R. Yom Tov Algazi (Bechoros 62b, 79): We find that Rav Ashi sent the money for Pidyon ha'Ben through a Shali'ach. The primary Mitzvah is giving the money to a Kohen, which can be done through a Shali'ach.

Chasam Sofer (YD 297): Shelichus of sending the father's money to a Kohen is like sending it on a monkey. All agree that Shelichus works for this. Poskim argue about a Shali'ach who gives his own money, without acquiring it for the father. The questioner in the Rivash was sure that this does not work. Many erred greatly about this.

Chazon Ish (YD 185 DH Kidushin): Even with a Shali'ach's money, the father redeems, unless he tells the Shali'ach to redeem. Then, the Shali'ach does the Mitzvah, even if it is the father's money.

Pischei Teshuvah (16): One can redeem through a Shali'ach. One can redeem on Tanai, and Tanai works only for matters to which Shelichus applies (YD 234:2).

Chasam Sofer: If the father gives five Sela'im to someone who is Zocheh for the Kohen, he was Yotzei. This is unlike Pidyon Peter Chamor, for there, the Yisrael has no Acharayus (responsibility for any loss). Here, the father has Acharayus until it reaches the Kohen or one who is Zocheh for him. Then, he did his Mitzvah.

Shach (CM 382:4): If Reuven had a son to circumcise, and Levi did it, he must pay him 10 gold pieces. However, if Reuven asked Shimon to circumcise, and Levi circumcised, he is exempt.

Tevu'os Shor (14): What is the Shach's proof from the Rosh, who compared Milah and Kisuy? The Shach should have the same Safek about Kisuy! What is his proof from the Rambam and Kidushin 29a? All know that the Mitzvah is on the father, and on the Shochet. Even so, he can make a Shali'ach, for one's Shali'ach is like himself. Darchei Moshe questioned the Or Zaru'a for this reason.

Ketzos ha'Choshen (2): I answer that the Rosh clearly shows that Shelichus does not help for the Mitzvah of Milah, which is on the father. If it did, just like one who stole the Mitzvah from the father must pay 10 gold pieces, the same would apply to one who stole the Mitzvah from the father's Shali'ach, since he is like the father! Rather, there is no Shelichus.

Ketzos ha'Choshen: The Or Zaru'a says that if a father knows how to circumcise, he may not let another circumcise. Darchei Moshe (YD 264:1) asked that one may make a Shali'ach in place of himself! The Tosfos Rid answers this. Shelichus does not help for a Mitzvah on the body. This refutes Tevu'os Shor's proofs. Ploni may make a Shali'ach to affix a Mezuzah, and Ploni will sit in the house. The Torah imposed Kisuy on the Shochet, and Milah on the father. It is like Tefilin, Sukah and Tzitzis, for which Shelichus does not help. There is no Shelichus to eat something. Yibum of another brother is not Shelichus. The Kolbo (Hilchos Berachos, Sof ha'Sefer) says that there is no Shelichus for Kisuy. One who can circumcise should do so himself. Sucking out the blood is only for Refu'ah, so one may honor another to do it.

Ha'Makneh (Kidushin 29a b'Tosfos DH Oso): The Shach holds that the Mitzvah of Kisuy ha'Dam is on the Shochet himself. However, perhaps a father is merely commanded to arrange the Milah, like the Ramban and Ritva say. The Shach learned from the Rosh, who compares Milah to Kisuy ha'Dam, i.e. the Mitzvah is to circumcise. The Shach criticized those who honor others with the Mitzvah, but not if the father makes a Shali'ach. This refutes all Tevu'os Shor's proofs regarding Mitzvos done through a Shali'ach.

Yad Eliyahu (51): The Rambam (Hilchos Klei ha'Mikdash 4:7) says that a Kohen (Aharon) may let another Kohen offer Aharon's Korban, even though it is Aharon's Mitzvah. We must say that it is because one's Shali'ach is like himself, even though it is better to do the Mitzvah himself. The Rosh connotes unlike the Shach. The Rosh says that it depends on the father's desire, even if he is a Mohel! The Taz brings from the Ran, who explicitly says so. All the Mitzvos that a man must do for his son, e.g. to teach him Torah and a trade and to swim, and to marry him off, were taught with Milah and Pidyon. All are possible through a Shali'ach. Pesachim 7b says that the father must circumcise. I.e. the Mitzvah is incumbent on him. We said similarly about Shechitas Pesach and Kodshim, which can be done through a Shali'ach. The Medrash Tanchuma says that Hash-m did for Yisrael what a father must do for his son. E.g. he circumcised them through Yehoshua. Why does the Shach permit Pidyon l'Chatchilah through a Shali'ach?