Prayer: Property Purchased with Money Lacking Khums
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 860
If a person purchases property with money on which khums has not been paid and the purchase is a non-specified undertaking,[1] as most purchases are, then using it is lawful for him and he owes khums on the money he paid for the property. However, if a person purchases property with the actual money on which khums has not been paid,[2] then using that property without the authorisation of a fully qualified jurist is unlawful; and based on obligatory precaution, prayers performed there are invalid.
-Ayatullah Sistani, Practical Laws of Islam, Prayer (Salah)
See the first footnote pertaining to Ruling 807 for an explanation of this term.
This is known as a ‘specified’ (shakhṣī) purchase. See the second footnote pertaining to Ruling 807 for an explanation of this term.