פירוש על עבודה זרה 41:6

The Talmud raises a problem, that renting a field to a non-Jew is prohibited even in Syria, even though this is a decree made on a decree. The resolution is that this mishnah considers Syria to be part of Israel even though it was only conquered by an individual (David). Thus the rules concerning selling them land could apply in principle. When it comes to renting them a field, the rabbis ruled strictly because there are two problems (giving them a foothold and tithes), but renting a house, where there is only one problem (giving them a foothold), is permitted.