The World Federation One Stop Fiqh

Ruling 1778

If a person purchases something and after agreeing the transaction he pays for it with money on which khums has not been paid,6 the transaction is valid but he will be indebted to those entitled (mustaḥiqqūn) to receive khums for the khums on the money he paid to the seller.

6 This is referring to a type of purchase that is known as a ‘non-specified undertaking’. See the first footnote pertaining to Ruling 807.