Our Gemara tells of Rav Mari bar Raḥel who lent money to a non-Jew and was holding – and living in – a house belonging to the non-Jew that acted as a guarantee on the loan. The non-Jew sold the house to Rava. After a year Rav Mari bar Raḥel approached Rava in order to pay rent, explaining that the house was mortgaged to him for a year, during which time the non-Jew could not have removed him from the house. From this point on, however, Rava became the full owner of the house and Rav Mari bar Raḥel wanted to pay him. In response, Rava said that had he known the circumstances he would not have purchased the house, but since he had bought it from the non-Jew he would keep their rules and allow Rav Mari bar Raḥel to continue living in the house without payment until the loan was paid.
It should be noted that such an arrangement would be considered ribit – forbidden interest – under Jewish law, since Rav Mari bar Raḥel was receiving free rent in addition to repayment of the loan. Rashi explains that it is permitted in this case since there is no real relationship between Rava and Rav Mari bar Raḥel – the relationship is between them and the non-Jew. The Ra’avad suggests that since Rav Mari bar Raḥel received his rights from a non-Jew, he can be treated as such, and under non-Jewish law this relationship is not considered interest, but a long-term sale.
Rav Mari bar Raḥel was a fourth generation Babylonian amora. It appears that he was the son of a non-Jew named Issur who had kidnapped and married Raḥel, the daughter of the great amora, Shmuel. After a time, Issur converted and was considered an upstanding member of the Jewish community. Nevertheless, since Mari had been conceived prior to Issur’s conversion, Mari is introduced to us in the Gemara as his mother’s son, rather than his father’s. Mari was a scholar of renown and we find him quoting Torah in the name of several different teachers, although he had a particularly close relationship with Rava, who played a role in preparing him for a position on communal leadership.