Responsa על בבא קמא 226:6

Q. A owes money to B and B owes the same amount to a Gentile. B told A, in the presence of the Gentile, to pay his debt directly to the Gentile. The Gentile released B and depended upon A for payment. A successfully avoids payment to the Gentile because of an old debt due him from the latter. Since, according to Jewish law, the transaction was not valid and A's indebtedness to B was not legally transferred to the Gentile, A must pay his debt to B. But why should B be permitted to rob the Gentile? Is not robbing a Gentile prohibited? Moreover, the Gentile presses A for payment and eventually may force A to pay him his money; must A pay his debt to B?
A. Robbing a Gentile is prohibited, but one is permitted to annul a Gentile's debt (if he can do so by using plausible excuses and without causing the name of the Lord to be profaned). But, if A will be forced to pay the debt to the Gentile, he will not have to pay anything to B.
SOURCES: Cr. 227; Pr. 327; L. 385; Am II, 119.

Q. A owes money to B and B owes the same amount to a Gentile. B told A, in the presence of the Gentile, to pay his debt directly to the Gentile. The Gentile released B and depended upon A for payment. A successfully avoids payment to the Gentile because of an old debt due him from the latter. Since, according to Jewish law, the transaction was not valid and A's indebtedness to B was not legally transferred to the Gentile, A must pay his debt to B. But why should B be permitted to rob the Gentile? Is not robbing a Gentile prohibited? Moreover, the Gentile presses A for payment and eventually may force A to pay him his money; must A pay his debt to B?
A. Robbing a Gentile is prohibited, but one is permitted to annul a Gentile's debt (if he can do so by using plausible excuses and without causing the name of the Lord to be profaned). But, if A will be forced to pay the debt to the Gentile, he will not have to pay anything to B.
SOURCES: Cr. 227; Pr. 327; L. 385; Am II, 119.

Q. A owes money to B and B owes the same amount to a Gentile. B told A, in the presence of the Gentile, to pay his debt directly to the Gentile. The Gentile released B and depended upon A for payment. A successfully avoids payment to the Gentile because of an old debt due him from the latter. Since, according to Jewish law, the transaction was not valid and A's indebtedness to B was not legally transferred to the Gentile, A must pay his debt to B. But why should B be permitted to rob the Gentile? Is not robbing a Gentile prohibited? Moreover, the Gentile presses A for payment and eventually may force A to pay him his money; must A pay his debt to B?
A. Robbing a Gentile is prohibited, but one is permitted to annul a Gentile's debt (if he can do so by using plausible excuses and without causing the name of the Lord to be profaned). But, if A will be forced to pay the debt to the Gentile, he will not have to pay anything to B.
SOURCES: Cr. 227; Pr. 327; L. 385; Am II, 119.