Gemara

(Beraisa): If a man died, leaving his orphans money of Ribis that he collected, even if they know this, they need not return it. If he left them a cow, garment or any specific item, they must return it for his honor.

Question: One need not honor such a father! "Do not curse a Nasi of your nation" - one who acts like your nation (but one need not honor a Rasha)!

Answer: We answer like Rav Pinchas answered (elsewhere). The case is, the father repented and died before he was able to return it.

Kidushin 32a (Rav Yehudah): One must honor his father from his own money.

(Rav Noson bar Oshaya): He honors using his father's money.

R. Yirmeyah asked, and was told to follow R. Noson's opinion.

Question (Beraisa): It says "honor your father and mother", and "honor Hash-m from your wealth." Just like one must spend money to honor Hash-m, also to honor parents.

Answer: He must spend time and neglect his job to honor them.

(Beraisa): A son may feed his (poor) father Ma'aser Oni.

Question: If the son must spend to honor his father, how can he fulfill his obligation with Ma'aser Oni?!

Answer: He must use his own (Chulin) money to feed the father the basics. He may use Ma'aser Oni only for extras.

R. Yehudah says that one who does so will be cursed. Even if the Ma'aser Oni is only for extras, it is disgraceful.

Rishonim

Rif and Rosh (Kidushin 13a and 1:50): If a man lacks money and his son has, we force the son to give Tzedakah, and give it to his father.

Rosh: R. Chananel proved this from a case in the Yerushalmi in which R. Yonason forced a son to feed his father. This is a weak proof, for there, the father wrote his property to his son. He brought another proof from the Yerushalmi, which obligates Kivud Av v'Em even if the son does not have and must beg. It does not mean that he will spend his money and need to beg, for we hold that Kivud Av v'Em is from the father! Rather, one must honor him with his body, even if through this he is idle from his job and must beg. The Halachah is that Kivud Av v'Em is from the father's money. Also the She'altos says so.

Hagahos Ashri: A poor mother had three sons. One was poor, and merely subsisted from what he received for learning. Another had 16 gold pieces, and the third was not here. We hold that Kivud Av v'Em is from the father's money. The Rif wrote that we force the son due to Tzedakah. Presumably, this is only if he has, and need not beg. If they do not feed her, they are cursed. The Gemara connotes that that they may feed her from Ma'aser Sheni and accept the curse. Here is different. Since she has rich sons, we force them. When they have and want to feed her from Ma'aser, we do not protest, but they will be cursed. We cannot force them to give to her extras. It is a Mitzvah to do so.

Rambam (Hilchos Mamrim 6:3): Kivud Av v'Em is to give to eat, drink, clothe and cover from the father's money. If the father has no money and his son does, we force the son to feed his parents according to his means.

Rif (Bava Metzia), Rambam (Hilchos Malveh 4:4) and Rosh (Bava Metzia 5:5): If a man died, leaving money of Ribis that he collected, even if his heirs know this, they need not return it. If he left them a specific item, they must return it for his honor only if he repented and died before he was able to return it.

Mishneh l'Melech (DH v'Yesh): A child need not honor his parents in the matter his parents sinned with, even if his parents repented.

Rambam (6:11): One must honor and fear his father even if his father is a Rasha who transgresses.

Question (Tur): The Gemara (Bava Metzia 62a) says that if the father did not do Teshuvah, his children need not return a stolen cow that they inherited. This shows that one must honor his father only if he did Teshuvah, but not if he is a Rasha!

Answer #1 (Kesef Mishneh): The Gemara discusses a cow received for Ribis. It was not stolen. Only the lender is commanded about Ribis, not his son. If the father repented and wanted to return the cow but was unable to, it is as if his sons did not inherit it. Otherwise, it is the son's property, and we hold that one need not honor his father from his money. He must honor when there is no loss of money, even if the father is a Rasha.

Question #1 (Lechem Mishneh): If so, how can we answer for the opinion that one must use his money to honor his father? It is difficult to say that he establishes the Beraisa to be when he did not do Teshuvah.

Question #2 (Machaneh Efrayim Malveh 8): If a son does not return for Kivud Av v'Em, rather, for it is as if he did not inherit it, this should apply even when the father left money, and to any heir, not just children!

Question #3 (Taz YD 240:17): The Gemara asked that the son should not need to return the cow because the father is not "Amcha". The Kesef Mishneh exempts because it is the son's property!

Answer #2 (Machaneh Efrayim): Beis Din does not force one to fulfill Kivud Av v'Em, for the Torah specifies the reward. If the father left a specific item, we force, for then there is disgrace (Tosfos Kesuvos 86a DH Pri'as). If the father did not do Teshuvah, we are not concerned for disgrace.

R. Shimshon (Pe'ah 1:1 DH Yerushalmi): The Yerushalmi obligates Kivud Av v'Em even if the son must beg. It does not mean that he begs for food to give to them. Rather, he gives his food to them, and needs to beg for himself, like the opinion that Kivud Av v'Em is from the son. Rav Noson is forced to explain that he is idle from his job and must beg. He does not obligate the son to use his money even when the father has nothing, for we did not answer the question against him by saying that it is when the father has no money.

Poskim

Shulchan Aruch (YD 240:5): One must feed his parents, i.e. from their money. If a man has no money and his son has, we force him to feed his father according to his ability. If the son lacks, we do not force him to beg to feed his father.

Beis Yosef (DH v'Zeh): The Rif, Rambam, Rosh and Tosfos rule like Rav Noson, for Rabanan who instructed R. Yirmeyah hold like him. They are a majority against Rav Yehudah. Also, Rabanan ruled like this in practice.

Gilyon Maharsha (4, citing Shevus Yakov 1:75): A Kinyan to exempt one's son does not help. He cannot cast himself on the Tzibur.

Rema: Some do not obligate more than he must give to Tzedakah. In any case, if he can feed him from Chulin, but uses his Tzedakah, he will be cursed. If one has many sons, we calculate how much each must give according to their wealth. If he has rich and poor sons, we obligate only the rich ones.

Question (Taz 6): Why does he say 'some say that'? No one obligates giving more than he must give to Tzedakah!

Answer (Shach 6): The Darchei Moshe (1) derives from 'he need not beg' that if he would not need to beg, he must suppy all their needs, even though surely one need not do so for Tzedakah. Semag and Semak are stringent, but the Rambam holds like the Shulchan Aruch says.

Tosfos (31a DH Kaved): The Yerushalmi expounds "honor Hash-m from your wealth" (from money you have), but one must "honor your father and mother", even if he has no money and must beg to feed them.

Gra (11): Do not say that when the father has no money, the son must use his own. If so, we should have answered the question against Rav Noson by saying that it is when the father has no money!

Gilyon Maharsha (7,8): The Rashba (3:44) obligates a son to pay his father's debt, even if he did not inherit anything. The Shulchan Aruch (CM 107:1) says that there is no Mitzvah to do so.

Shulchan Aruch (ibid): One must honor him with his body, even if through this he is idle from his job and must beg. This is if the son has food for that day. If not, he need not abandon his job and beg.

Source (Beis Yosef DH u'Mah she'Chosav Rabeinu): R. Yerucham says that we learn from Kavod Hash-m. One need not neglect his job to visit the sick or console mourners if then he will need to beg.

Gra (14): This is astounding! The Yerushalmi holds that Kivud is from the son's money, and the Bavli explicitly obligates abandoning his job and begging, for honoring parents is equated honoring Hash-m.

Mayim Amukim (2:101): If one was renting in his son's (Levi's) house, and Levi swore to sell it to Yehudah, the oath is invalid, for it is against Kivud Av v'Em.