פירוש על קידושין 63:1

From whose: Does he give him food and does he give him drink.

Rav Yehuda says, "From that of the son": RI (Rabbi Yitzchak) was precise, according to the one that holds it is from that of the son - what should one do if he was confronted by the honor of his parent, his own lost object and the last object of his fellow [all at the same time]? If he occupies himself with the honor of his parent, does not the lost object of his fellow take precedence? As we say in [the chapter entitled] Elu Metziot (Bava Metzia 32a), "Perhaps [if] his father said to him, 'Do not return [it],' perhaps he should listen to him? [Hence] we learn to say, etc." And this, "Do not return," is that he says, "Occupy yourself with my honor." For [regarding], "Do not return," for nothing, I do not need a verse! It is therefore implied that the lost object of his fellow takes precedence over the honor of father and mother. But if he occupies himself with the lost object of his fellow, behold his lost object takes precedence! As it is written (Deuteronomy 15:4), "However, there will not be among you any needy one" - yours is before [that of] all people (Bava Metzia 30b, 33a). And if he occupies himself with his lost object, behold the honor of his parent takes precedence, according to the one that holds it is from that of the son. So it appears to RI that he should leave the honor of his parent and the lost object of his fellow and occupy himself with his [own] lost object. For that which it said that the honor of a parent takes precedence is only when he allows his parent to do what he wants with his money. For this is the crux of honor. But with his lost object: Since the parent does not benefit from the lost object itself, the son is not obligated to lose his lost object because of his parent. And even though we say adjacently, "Such that he takes a purse and throw it into the sea, and the son does not embarrass him" - according to the one that holds it is from that of the son, it is speaking there about such a manner in which the father derives pleasure from it. For example, he throws it into the sea to cause fear among the people of his household. For if it were not thus - if he throws it into the sea for nothing, he is wicked; as he transgresses, do not waste! And even when it is inadvertent and he throws it in his anger, he nevertheless derives pleasure from throwing his purse. And because of that, one may not embarrass him.

The Sages gave this ruling to Rav Yirmeyah, "It is like the one who says it is from that of the father": It is implied that this is the law. And so did Rav Achai Gaon decide in his Sheiltot in Parashat Vayishma (The end of Section 57). But he [also] decided that when the father does not have and the son has, the son is obligated to feed his father. And so did RI and Rabbenu Chananel decide - that if the father has no money but the son has, the son must sustain his father from that which is his. For he is no less than another [who is needy]. It is as it said in [the chapter entitled] Naarah SheNitpatetah (Ketuvot 49b) that Rav forced that man and extracted four hundred zuz for charity. Moreover, we say in the Yerushalmi, "Rabbi Yose said, 'Were it only so, that all of my teachings were as clear as that which we force a child to sustain his parent.'" And there is another proof from that which it said in the Yerushalmi that Rabbi Yochanan and Rabbi Yoshayah were walking on the road. A man came and kissed the feet of Rabbi Yochanan. [Rabbi Yoshaya] said, "What is this?" He said to him, "Because I said to him,' Go and yell in the synagogues,'" meaning I taught him that he should do so much, so that his son will sustain him. He said to him, "Why did the master not force [the son to sustain him]?" [Rabbi Yochanan] said to him in wonderment, "We force in something like this?" He said [back], "Did you not know that we force? It is obvious that we force." And there is another proof from the Yerushalmi that I brought before (Tosafot on Kiddushin 31a, s.v. Kaved): "Honor the Lord with your wealth" - if one has money, he is obligated; but if not, he is exempt. But with the honor of father and mother, it is stated, "Honor your father and your mother"; so it implies whether he has money or whether he does not have [it].

The rabbis dispute who must pay, but ultimately the majority holds that the parent must use his own funds to provide for himself. I should note that this section assumes that both parties have resources.