Chametz of a Gentile over which Pesach has passed, [deriving] benefit from it is permitted; but [chametz] of a Jew, [deriving] benefit from it is forbidden —- since it is said: Nor shall leaven be seen with you (Exodus 13:7).

[If] a Gentile lent [money] to a Jew on his chametz, [then] after Pesach [deriving] benefit from it is permitted. But [if] a Jew lent [money] to a Gentile on his chametz, [then] after Pesach [deriving] benefit from it is forbidden.  [If] a ruin collapsed over chametz, it is regarded as removed. Rabban Gamliel says: Provided a dog cannot search it out.