Ruling 2364
It is not necessary that the parties say a particular formula (ṣīghah) [for a gratuitous loan agreement to be valid (ṣaḥīḥ)]. For example, if a person gives clothing to someone with the intention (qaṣd) of a gratuitous loan and the latter accepts it with the same intention, it is valid.
-Ayatullah Sistani, Practical Laws of Islam, Gratuitous Loan (ʿĀriyah)