The World Federation One Stop Fiqh

Ruling 2183

A person who gives something on rent (muʾjir) and a person who takes something on rent (mustaʾjir) must be of the age of legal responsibility (bāligh) and sane (ʿāqil). They must also enter into the rental agreement of their own volition (ikhtiyār) and have right of disposal over their property. Therefore, someone who is foolish with finances (safīh)2 cannot rent anything nor give anything on rent as he does not have right of disposal over his property. Similarly, someone who has been proclaimed bankrupt (mufallas) cannot give on rent any property over which he does not have disposal, nor can he rent anything with that property. However, he can give himself on hire [as a worker].

2 Ruling 2091 provides further clarification of this term: it refers to someone who spends his wealth in futile tasks.