[Residing in a House Without Stating the Rent]

Answer—and Allah grants success: The man from whom rent is demanded—if his custom is leasing (his property)—then the resident owes the rent; but if that man has no custom of leasing, then he has no rent (due to him).
Hence the jurists of the school said: “The default ruling for benefits is permissibility.” We depart from this default in the case of one whose custom is leasing, following the general custom—namely, what Muslims practice in hotels, apartments, and houses prepared for rent in cities and markets and the like. Whoever resides in a hotel apartment or a (rented) room is held liable for rent, even if there was no mention between the parties of rent or of leasing; no one is excused for leaving off rent on the pretext that rent was not mentioned and that the default for benefits is permissibility.
The evidence for their statement “the default for benefits is permissibility” is that permission to enjoy a benefit is a permissive pathway that suffices for the lawfulness of enjoying it, without anything further. This is a matter well known among people, about which they scarcely differ.
Custom (ʿurf) is a Sharʿī pathway in the domain of transactions so long as texts do not contradict it—thus have the scholars set it forth.
The evidence for the soundness of what they have said is that Islam came while people engaged in buying and selling, leasing, profit-sharing, gifts, vows, lending for use, and so on; it approved them upon what they were doing, and only forbade specific particulars and matters, remaining silent about the rest.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2