Prayer: Purchasing Prayer Clothing with Unpaid Khums
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 807
If a person purchases clothing with money on which the one-fifth tax (khums) has not been paid, and the purchase is a non-specified undertaking (al‑kullī fī al‑dhimmah),[1] as most purchases are, the clothing will be lawful (ḥalāl) for him. However, because he used money on which khums had not been paid, and he delayed paying the khums that was due on it, he will have sinned and must pay khums on the money he gave to the seller. However, if a person purchases clothing with the actual money on which khums has not been paid,[2] then performing prayers with that clothing without the authorisation of a fully qualified jurist (al‑ḥākim al‑sharʿī) is ruled to be the same as performing prayers with usurped clothing.
-Ayatullah Sistani, Practical Laws of Islam, Prayer (Salah)
This refers to a purchase in which the actual thing with which the payment is made is not specified. For example, a buyer purchases some goods for £20 without specifying to the seller that he is purchasing the goods with a particular £20 note.
This is known as a ‘specified’ (shakhṣī) purchase and is not common. Here, the transaction takes place over money that has been singled out for that purchase. For example, a buyer tells the seller that he is purchasing the goods with such and such £20.