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.