Gemara

84a (Mishnah - R. Akiva): If Levi died, leaving a widow, a creditor and heirs, and someone else had a deposit from Levi or owed a loan to him, the heirs get it.

86a - Question (Rav Kahana): You (Rav Papa) hold that it is a Mitzvah to pay a debt. If the borrower says 'I do not want to do the Mitzvah', what happens?

Answer (Rav Papa - Beraisa): Forty lashes apply to Chayavei Lavin. If one refuses to do a Mitzvas Aseh, e.g. to make a Sukah or take a Lulav, we lash him until he fulfills it or until he dies.

91b: A man owed 100 Zuz. He died, and the only land he left was a plot worth 50 Zuz. The creditor took it as partial payment. The orphans gave him 50 Zuz (and took the land back); the creditor took it again for final payment.

(Abaye): It is a Mitzvah for orphans to pay the debt of their father. The 50 they gave the creditor was l'Shem Mitzvah. The creditor was entitled to take the land again.

This is only if the orphans did not say that the 50 Zuz is the value of the land. If they said this, they expel him from the land (and he cannot collect any more, since the father didn't leave any other land).

Bava Basra 157a (Mishnah): Yakov's heirs say that Levi died first, and Levi's creditors say that Yakov died first (so they can collect from what Levi inherited from him).

Inference (Rav Chana): This shows that a lender can collect property that the borrower later bought and sold or bequeathed. If not, even if Yakov died first, Levi's heirs would inherit, and the creditors would not collect!

Rejection (Ze'iri): The creditors do not collect due to the lien, rather because it is a Mitzvah for orphans (and all heirs) to pay the debt of their father (the one they inherited from).

Defense (Rav Ashi): If there were no lien in such a case, there would be no Mitzvah to pay the father's debt from the land, just like there is no Mitzvah to pay the father's Milveh Al Peh (a loan without a document)!

(Rav and Shmuel): A Milveh Al Peh cannot be collected from one who inherited or bought from the borrower.

Erchin 22a (Rav Nachman): At first, I never collected from orphans' property. After I heard that Rav said that orphans who consume others' (i.e. creditors') property should follow their father (i.e. die), I collect from their property.

(Rav Papa): At first he did not collect because paying a creditor is a Mitzvah. (Minor) orphans are not obligated to observe Mitzvos.

(Rav Huna brei d'Rav Yehoshua): He did not collect out of concern for Tzrari (perhaps their father gave money to the lender, to ensure that he will be paid).

They argue about when the father admitted (right before he died) that he still owes, or if he was excommunicated for not paying and died in Niduy.

The Halachah follows Rav Huna brei d'Rav Yehoshua.

Rishonim

The Rif and Rosh (Kesuvos 50a and 10:5) bring the Gemara in Kesuvos:

Ran (DH Mitzvah): It is a Mitzvah for orphans to pay their father's debt due to Kivud Av. We do not force them, because it is not an explicit Mitzvah like Sukah or Lulav. It is mid'Rabanan. The creditor was allowed to take the field again for final payment because he had a lien on the borrower's property. Had they told him that they pay to buy the land, not to pay the debt, he would not collect again. Rashi and others learn from here that we do not force them to pay their father's debt. If we did, in any case they would need to pay the rest of the debt! This is unlike R. Chananel.

Beis Yosef (EH 100 DH veha'Ran): Perhaps R. Chananel discusses after the enactment to collect from Metaltelim of orphans.

Rosh (9:13,14): Rav Papa says that paying creditors is a Mitzvah, and therefore minors are exempt. This implies that we force adults. This is when they inherited land. If they inherited Metaltelim, it is a Mitzvah but we do not force them. Rashi says that we do not force people to do Mitzvos mid'Rabanan. This is wrong. Rather, Beis Din does not force for Mitzvos, such as Kibud Av, for which the reward is explicit in the Torah. Latter Rabanan enacted that a creditor collects Metaltelim (of orphans). Creditors rely on Metaltelim like on land, so we force even if they inherited Metaltelim. This is the practice.

Hagahos Ashri (10:5): If the orphans are adults, we beat them until they (fulfill their Mitzvah or) die! If they are minors, they are exempt from Mitzvos! It seems that they are minors. The case is, their father admitted that he owed, or he died in Niduy (for refusal to pay). It seems that Abaye holds like Rav Huna brei d'Rav Yehoshua.

Hagahos Ashri (9:14): The Ri says that if they did not inherit anything, it is a Mitzvah but we do not force them. However, we hold like the opinion that a child is not obligated to honor his parents from his own money.

Ran (ibid.): According to the opinion that Shi'abud (the lien on a borrower's property) is mid'Oraisa, we force them to fulfill the Mitzvah of paying a creditor, just like we force one who refuses to take a Lulav. Perhaps we take his property. It is better to enforce the Mitzvah through his property than by forcing him bodily. According to the opinion that Shi'abud is not mid'Oraisa, we force the borrower himself and take his property, but we do not force his orphans when he is not here. For them it is only a Mitzvah mid'Rabanan.

Ran (ibid.): Rishonim say that the Mitzvah mid'Rabanan is only when the orphans inherited Metaltelim. There is no Mitzvah to pay from their own money. Here, they paid 50 Zuz from their father's Metaltelim. We learn from Bava Basra (157a). There, we tried to prove from a Mishnah that creditors collect from property that the borrower later acquired and bequeathed to others. Ze'iri dispelled this; perhaps the orphans pay the father's debt because it is a Mitzvah! If this Mitzvah applies even if they did not inherit property, it would not matter who died first! This connotes that we force orphans! However, perhaps this was the Havah Amina. We asked from Rav and Shmuel, who say Stam that a Milveh Al Peh is not collected from heirs. Therefore, we concluded that we do not force due to the Mitzvah to pay one's father's debt. However, the Rashba says that if they did not inherit Metaltelim, there is a Mitzvah to pay the father's debt, but we do force them. Our Gemara discusses when they inherited only the plot of land. If they inherited Metaltelim, we force them. This is the case in Bava Basra, which discusses forcing. When the orphans said that they give the money for the land, this is like land they bought themselves. Also a later creditor cannot seize it.

Rambam (Hilchos Malveh 11:8): It is a Mitzvah for orphans to pay the debt of their father from the Metaltelim that he left for them. If the heir does not want to, we do not force him. If the creditor seized (Metaltelim) in the father's lifetime, he collects from them.

Rambam (18:10): If Reuven owed Shimon 200 and left one field worth 100, and Shimon took it and the orphans gave him 100 from the Metaltelim they inherited and took the land back, Shimon can take it again for final payment. The 100 that they gave Reuven was a Mitzvah; it is a Mitzvah for orphans to pay the debt of their father. If the orphans said that the 100 is the value of the land, he cannot collect it again for his debt.

Poskim

Shulchan Aruch (CM 107:1): It is a Mitzvah for orphans to pay the debt of their father. If he left land, we force them just like we would have forced the father. If he left only Metaltelim, we do not force them to pay his debt, but it is a Mitzvah.

Beis Yosef (DH v'Zeh): The Rashba says that if the heirs themselves owe money and they inherited Metaltelim, the Mitzvah to pay their own debt comes first. If the orphans are not here, we do not take their property. In Kesuvos 84a and 92a, orphans were not forced to pay from Metaltelim that they inherited. We must say that they were minors, were not here, or they themselves owed others. If not, we force them with sticks.

Urim (4): Even if they inherited from an uncle, or any relative whom they need not honor, it is a Mitzvah to pay the debt, lest their uncle be a 'Rasha who borrows and does not pay.'

Shulchan Aruch (ibid.): This is letter of the law. Nowadays, after Ge'onim enacted that a creditor collects inherited Metaltelim, in every such case we force orphans to pay, even a Milveh Al Peh. An heir is in place of his father. Similarly, they must pay from money that was owed to their father, even if they collected Metaltelim. If they did not inherit anything, there is not even a Mitzvah to pay their father's debt.

Rema: If one inherited a small amount, he need pay only what he inherited.