Gemara

(Beraisa) Suggestion: Perhaps Kibud Av va'Em overrides Shabbos!

Rejection: "A man will fear his parents, and keep My Shabbosos" - all of you (even your parents) must honor Me!

Suggestion: The parent told the child to slaughter or cook. If not for the verse, this would override a Melachah of Shabbos (which is Chayavei Kerisos)!

Rejection: No, he told the child to be Mechamer (make an animal work). This is a Lav (without Kares), yet it does not override Shabbos.

Question: We hold that an Aseh overrides a Lav. We should learn from here that it does not!

Answer #1: Perhaps Isurim of Shabbos are more stringent than regular Lavin.

Rejection: The following Tana does not distinguish!

(Beraisa) Suggestion: If a father told his son (a Kohen) to become Tamei (Mes), or not to return a lost object, perhaps he should obey!

Rejection: "Ish Imo v'Aviv Tira'u v'Shabsosai Tishmoru" - you are all obliged to honor Me.

Answer: Hechsher Mitzvah is different.

Bava Metzi'a 32a - Inference: If not for "Ish Imo v'Aviv Tira'u...", we would say that he should listen!

Question: Kivud Av v'Em is an Aseh. An Aseh does not override a Lav and an Aseh (Rashi - of Hashavas Aveidah; Tosfos 30a DH Ha) - of Tum'as Kohanim)!

Answer: Honor of parents is equated to honor of Hash-m. It says "Kaved Es Avicha v'Es Imecha", and "Kaved Es Hash-m". Therefore, one might have thought that he should listen. The verse teaches that he should not.

Rishonim

Tosfos (6a DH she'Chen): The Mitzvah of Kibud is giving food to a parent. Hechsherim, i.e. means to this end, do not override Lavin.

Rif and Rosh (Bava Metzi'a 17b and 2:28): One might have thought that if a father told his son to become Tamei, or not to return a lost object, he should obey. "Ish Imo v'Aviv Tira'u v'Shabsosai Tishmoru (Ani Hash-m Elokeichem)" - you are all obliged to honor Me.

Nimukei Yosef (DH Gemara): We learn from "Ani Hash-m".

Note: "Ani Hash-m" is in the text in Bava Metzi'a (32a), but not in Yevamos.

Rambam (Hilchos Mamrim 6:12): If one's father told him to transgress the Torah, be it a Lav or an Aseh or mid'Rabanan, he may not obey. "Ish Imo v'Aviv Tira'u v'Shabsosai Tishmoru" - all of you must honor Me!

Sefer ha'Mitzvos (Aseh 112, cited in Hagahos Maimoniyos 8): This shows that one does not become a Rasha through speech (telling someone to transgress). This is because the listener should obey the Rebbi (Hash-m), not the Talmid. If the father became a Rasha for this, we would not need a verse to teach that one does not obey! The only one punished for such speech is one who entices to serve idolatry.

Question (Kesav v'Chosam R. Akiva Eiger Bava Metzi'a 30a Tosfos DH Ha): Even if one who tells a stranger to transgress is a Rasha, there was a Hava Amina that Kivud Av v'Em overrides Isurim. If it did, one would be permitted to tell his child to transgress. Therefore, in any case we need a verse!

Rambam (Hilchos Gezeilah 11:19): If one saw an Aveidah and his father told him not to return it, he returns it and does not obey. If he would obey, while fulfilling Kivud Av he would Mevatel the Aseh "Hashev Teshivem" and the Lav "Lo Suchal Lehis'alem".

Magid Mishneh: This is even if the father tells the son not to return it so the son can honor him by bringing to him food.

Mishneh l'Melech: Had the father told the son not to return (without a proper reason, merely) to transgress, obviously he would not obey, for the father is a Rasha!

Drishah (CM 266:7): The Rif and Rosh only bring the reason given in the Beraisa, 'you are all obliged to honor Me.' They explain that the Mishnah discusses when the father told the son not to return without a reason. Then, it suffices to say that the son should honor Hash-m. The Rambam teaches that even if the father wanted the son to serve him, and by doing so he would also honor Hash-m by fulfilling Kivud Av v'Em, he returns the Aveidah because there is also a Lav.

Terumas ha'Deshen (40): Talmud Torah is greater than Kivud Av v'Em. A Kohen may go to Chutz la'Aretz for Talmud Torah, even though R. Yochanan was hesitant to permit this for Kivud Em. Yakov was not punished for neglecting Kivud Av v'Em while learning by Shem and Ever. If a son is confident that he will succeed to learn from a Rebbi in another country he should go, even if this pains and worries his father. Mora (awe) of parents is no greater than Kivud; it is also an Aseh.

Poskim

Shulchan Aruch (YD 240:15): If one's father told him to transgress Torah, be it a Lav or an Aseh or mid'Rabanan, he may not obey.

Beis Yosef (DH u'Mah she'Chosav): One does not obey even to transgress mid'Rabanan laws because "Lo Sasur" is an Asmachta for them, so they are included in Torah. Alternatively, mid'Rabanan laws also honor Hash-m, so one may not transgress them to honor his parent.

Yam Shel Shlomo (Kidushin 1:63): Even if there was no Asmachta, one must be more careful about mid'Rabanan laws than mid'Oraisa (Eiruvin 21b)! There is a Chayav Misah b'Yedei Shomayim for all mid'Rabanan laws!

Gra (26): The Gemara in Yevamos connotes that only Kares is not Nidcheh for Kivud Av v'Em. However, the Medrash Rabah (14:6) brings this after teaching that we do not follow a king's command to transgress, even though (normally) one who violates the king's command is Chayav Misah. We do not transgress any Devar Torah to honor a king, all the more so for Kivud Av v'Em! Tana d'vei Eliyahu (Sof Parashah 25) says that we honor a father except for (a command to do) an Aveirah, theft or something repulsive.

Yam Shel Shlomo (Kidushin 1:63, cited in Pischei Teshuvah 14): Some say that if one's father told him not to say Kaddish for his mother, he obeys, for the father's honor comes first. He should not obey (this is like the Rema 376:4).. There was an enactment to say 'I am an atonement for my parent' in the year of Aveilus. All the more so it is a Mitzvah mid'Rabanan to say Kaddish, which helps the Mes tremendously. Not saying it transgresses "V'Ohavta l'Re'echa Kamocha". However, one obeys a father's command not to wear black when mourning over his mother, which is a mere custom.

Rebuttal (Birkei Yosef): Even though Kaddish is based solidly on Medrashim, it is a mere custom. Perhaps this is like a son whose parents are divorced; he may decide whose honor he wants to put first.

Beis Lechem Yehudah (citing Sefer Chasidim): One should not fast optional fasts if it pains his parents. If Reuven was sick and doctors said that he should not eat or drink certain foods, and he threatens his son 'if you do not bring it to me I will not forgive you in this world or the next', the son need not obey.

Birkei Yosef: This is only if the food is dangerous for the father. If not, he should obey.

Or Some'ach (Milu'im after Sefer Mo'ed, Mamrim 6:12): Even though Kavod ha'Briyos overrides even a Lav mid'Rabanan, Kivud Av v'Em does not override mid'Rabanan laws. We find that Kavod ha'Briyos overrides Hashavas Aveidah, but Kivud Av v'Em does not.

Question (Shirei Korban Nazir 34a DH Od): Rav Shmuel holds that Kivud Av v'Em overrides Tum'ah mid'Rabanan (in the Yerushalmi Nazir 34a). The Bavli (Kidushin 31b) also records that R. Yochanan permitted Rav Asi to go to Chutz la'Aretz for Kivud Em (even though he was a Kohen and Chachamim decreed Tum'ah on Chutz la'Aretz). We hold that Kivud Av v'Em does not override even mid'Rabanan laws!

Shulchan Aruch (16): If one's father told him not to speak with Ploni or not to forgive him until a certain time and if not for this the son would be appeased immediately, he should not be concerned for his father's command.

Source (Teshuvas Rosh 15:5).

Taz (16): It is forbidden to hate a Yisrael unless one saw him transgress. Therefore, the father tells his son to transgress.