Gemara

Rabah and Rav Yosef were walking. Rabah said 'my Shevisah is under the date tree that supports another tree.'

Rav Yosef: I do not know that tree!

Rabah: You can rely on me!

(Beraisa - R. Yosi): If Reuven knew a particular place... Shimon says 'my Shevisah is with Reuven'...

Really, R. Yosi did not teach the Beraisa. Rabah said it in the name of R. Yosi in order that Rav Yosef would rely on it

Pesachim 112a - R. Akiva (to R. Shimon): If you want people to heed you, say [teachings] in the name of a great Chacham;

Berachos 27a - Question: How could R. Yirmeyah bar Aba pray in back of Rav?

(Rav Yehudah): One may not pray at the side of his Rebbi or in back of his Rebbi.

(Beraisa - R. Eliezer): The following cause the Shechinah to depart from Yisrael -- one who prays in back of his Rebbi... or says something that he did not hear from his Rebbi.

43b: Rav Papa blessed on myrtle, and then on oil.

Rav Huna brei d'Rav Ika: Don't you hold that the Halachah follows the arbiter (R. Gamliel, who says that we bless on the oil first)?

Rav Papa: Rava said that the Halachah follows Beis Hillel. (I did like him.)

Megilah 15a (R. Elazar): Whoever repeats something in the name of the one who said it brings redemption to the world - "Esther told the king in the name of Mordechai."

Gitin 20a (Beraisa - Rebbi): A Get written on Isurei Hana'ah is valid.

Levi taught this in Rebbi's name, and the audience was unreceptive. Levi taught this in the name of Chachamim, and the audience was receptive.

This shows that this is the Halachah.

Yevamos 71a (Rava): Yisra girded his sword and threatened anyone who challenges his tradition from Shmuel ha'Navi that an Amonis or Mo'avis is permitted.

Question: R. Aba taught that a Chacham is believed to teach a new law relevant to a case at hand only if he already taught the law before!

Answer: Yisra was believed, since Shmuel and his Beis Din were around.

Rishonim

Rosh and R. Yonah (Berachos 4:5 and 18b): One who says in the name of his Rebbi something that he did not hear from his Rebbi causes the Shechinah to depart.

Rashi (Berachos 43b): Rava did not really say that the Halachah follows Beis Hillel. Rav Papa merely wanted to spare himself from shame.

Maharlbach (p.279 DH u'Var, cited in Gilyon ha'Shas 43b): A Chacham must be "Modeh Al ha'Emes" (admit that his teaching is wrong), but not when he acted according to it, for that is a great embarrassment.

Tosfos (43b DH Hachi): The Rif rules like Rava. This connotes that 'this is wrong' was not in his text.

Note: Hagahos ha'Gra also deletes this from the text, and supports this from the Rif. Alternatively, the Rif could explain like the Rama (below).

(Rama mi'Piano 5): Rava did not say so. Due to humility, Rav Papa did not want to say that he argues with R. Yochanan, so he attributed it to Rava. Since he did so, surely he knew that this is the Halachah!

Rashbam (112a DH v'Im): R. Akiva taught that if you want people to heed you, learn from a great Chacham and say teachings in his name.

R. Chananel (112a DH Chamishah): He taught that if one has a question about Isur, he should ask a great Chacham and do like he says.

Note: Sefer ha'Aruch (Chanak, brought in the margin on 112a) explains like this regarding rulings that involve mortal issues.

Rashi (Gitin 20a DH Darshah and Alma): Levi taught the law in the name of Rebbi so that the audience will accept it. Since he tried so hard to get them to accept it, this shows that this is the Halachah.

Tosfos (20a DH mi'Shmei): The Gemara in 77a connotes oppositely! Rather, since the audience accepted that Chachamim (the majority) hold like this, this shows that this is the Halachah.

Nimukei Yosef (Yevamos 25a DH d'Ha, citing the Ritva): Rashi says that Yisra would not lie, for Shmuel and his Beis Din were around (so he could be disproved). Surely we do not suspect Chachamim of lying! Rather, we are concerned lest he reasons (and extrapolates) and thinks that he received the law. If his Rebbi is around, he will be precise.

Yosef Ometz (63): Some challenge the Ritva, for we find that Rav Papa falsely said that he heard from Rava! This is not difficult. Rav Papa knew the Halachah. One may do whatever is needed to establish the correct Halachah. Surely one may not do so just to defend something he already did.

Poskim

Shulchan Aruch (YD 242:24): One may not say something he did not hear from his Rebbi until he says the one who said it.

Bach (7): The Rosh and R. Yonah say that the Gemara forbids saying in the name of one's Rebbi something that he heard from someone else. This is difficult. They connote that he may say it Stam. Chachamim exhorted that one must say something in the name of the author! If he did not hear this from anyone, just he thought of it himself, what is wrong if he says it Stam? The Rambam's Perush is correct. He heard it from someone else, and says it Stam. Chachamim warned against this; it causes the Shechinah to depart.

Magen Avraham (OC 156:2): If one heard a law and it seems that the Halachah follows it, he may say it in the name of a great Chacham, so people will accept it (Eruvin, Pesachim). However, one who says something in the name of a Chacham from whom he did not hear it, causes the Shechinah to depart! This requires investigation. One who says something, but does not say from whom he heard it, transgresses a Lav, like it says in Nedarim.

Eliyahu Rabah (156:2): We can say that Maseches Kalah (it is like the Beraisa in Berachos) discusses when it would have been accepted in the author's name. Alternatively, Eruvin 51 discusses one who heard a teaching Stam, but if one heard from a Chacham, he may not say it in the name of another Chacham. Also, it seems that the Isur to attribute to another Chacham is only what one says based on his own reasoning, but if he heard it from a Chacham, he may say it in the name of another Chacham.

Machatzis ha'Shekel: One could explain the Gemara in Berachos to forbid saying anything he did not hear from his Rebbi, like R. Eliezer, who never did so (Sukah 27b). Surely this is not correct. It was mere Midas Chasidus of R. Eliezer. We cannot say that not doing so causes the Shechinah to depart. Most Tana'im and Amora'im did not do so.

Eshel Avraham: In practice, this requires investigation.

Machatzis ha'Shekel: Divrei Chamudos (Berachos 4:24) says 'if one will say Stam something he did not hear from his Rebbi, perhaps it is wrong, and people will look down on the Rebbi. Therefore, the Gemara says that if you want people to heed you, say in the name of a great Chacham.' I.e. since the Isur is lest the Rebbi be disgraced, it is permitted if one knows that the Halachah follows the teaching. Alternatively, if he knows that the Rebbi would not object, it is permitted l'Shem Shamayim. Pesachim 112 discusses such a case. I did not find what the Magen Avraham cites from Nedarim. In Megilah and Pirkei Avos (6:6) we find that saying something in the name of the author brings redemption to the world.

Shirei Korban (Yerushalmi Nazir 34a DH Eisunei): The Magen Avraham's question is difficult only for Rashi (who explained Pesachim 112a simply), but not for the Rashbam. We can say that Rashi discusses saying Agados and worldly matters, but not Halachos. In Eruvin, we can say that after Rav Yosef relied on what Rabah said, Rabah revealed that it was a Stam Beraisa, and not in the name of R. Yosi. Alternatively, one may not attribute to his Rebbi a Halachah that he derived himself, but if he heard it Stam, he may. Rashi's Perush in Berachos, that Rava retracted, is fine. In Berachos 27a, why did we challenge R. Yirmeyah first from an Amora, and afterwards from a Beraisa? Rashi holds that the Beraisa is an individual's opinion (R. Eliezer), and the Halachah does not follow it, including the Isur to say what one did not hear from his Rebbi. R. Eliezer himself fulfilled this. R. Yonah says that the Beraisa forbids saying what one did not hear from his Rebbi in the name of his Rebbi. This is like the Rif's text, which attributes the Beraisa to R. Eliezer Ben Chisma.

Rebuttal (Kuntres Acharon of Machazik Berachah OC 156:7): R. Eliezer knew that the other Tana'im said Halachos that they did not receive from their Rebbeyim. He would not say that they distance the Shechinah!

R. Akiva Eiger (on Shulchan Aruch): The Medrash Tanchuma (Bamidbar 27) expounds "Al Tigzal Dal" to forbidden saying a teaching not in the name of the author.

Birkei Yosef (242:29): Ge'onim say that if one knows that the Halachah follows a teaching, and people will not accept it from him, he may say it in the name of his Rebbi, so that people will accept it. If he is unsure whether it is the Halachah, he may not attribute it to his Rebbi.

Ha'aros on Birkei Yosef (18): We can say that R. Yonah forbids saying in the name of his Rebbi what he did not hear from him. This is brazen. Pesachim 112 permits saying things in the name of a Chacham who is not his Rebbi. The Ge'onim (Chemdah Genuzah 102, in Otzar ha'Ge'onim Berachos 165) explicitly permit in the name of one's Rebbi, i.e. if he knows that it is correct. It is forbidden only when he is unsure if the teaching is correct, and says it in the name of his Rebbi so that people will accept it.

Birkei Yosef (OC 216:12 DH v'Efshar): It is difficult to say that Rav Papa knew that he erred, and to defend himself and spare himself shame he said that Rava said so. He should have admitted to the truth, lest the Halachah be fixed incorrectly! Rather, he was sure that he is correct, but he was ashamed to say that he himself argues with R. Yochanan, therefore he attributed it to Rava, so people would accept it. Pesachim 112a permits this. We rule like Rav Papa, for he is Basra.

Machazik Berachah (OC 156:7): The Beraisa in Kalah and Berachos discusses a total Talmid. The Gemara answered that R. Yirmeyah bar Aba was a Talmid Chaver. This shows that the Beraisa discusses a total Talmid. Once a Talmid is qualified to rule, he may attribute teachings to a bigger Chacham if he knows that the Halachah follows it. Tosefes Shabbos says that the Beraisa forbids when he himself knows that what he says is wrong, but he has a need to say it. I disagree.

Kuntres Acharon (ibid.): R. Akiva told R. Shimon to attribute his teachings to a great Chacham. This was at the end of R. Akiva's life (he was imprisoned), and R. Shimon was already qualified to rule.

Afarkasta d'Anya (4, Inyanim Shonim 372:2): The importance that the correct Halachah be received overrides the importance of saying teachings in the name of the author.

Afarkasta d'Anya (ibid., 2): The Isur to say teachings not in the author's name is even if the author pardons this.