If a person does not know whether a transaction (muʿāmalah) he has conducted is valid (ṣaḥīḥ) or invalid due to him not knowing the ruling (masʾalah), he cannot have disposal over what he received in the transaction nor what he handed over; rather, he must learn the ruling or exercise precaution (iḥtiyāṭ), albeit by means of a settlement (muṣālaḥah).
However, if he knows that the other party consents to him having disposal over the item even though the transaction is invalid, then having disposal over it is permitted (jāʾiz).