Ruling 2367
It is not valid if a child, insane person, or someone who has been proclaimed bankrupt (mufallas) or is foolish with finances (safīh)[1] lends out his property. However, it is not a problem if the guardian (walī) deems it a matter of primary importance and lends out property belonging to someone over whom he has guardianship (wilāyah). Similarly, there is no problem in a child merely being an intermediary for delivering the property to the borrower.
-Ayatullah Sistani, Practical Laws of Islam, Gratuitous Loan (ʿĀriyah)
1
Ruling 2091 provides further clarification of this term: it refers to someone who spends his wealth in futile ways.