Who is responsible for paying Fitr (Zakat al-Fitr) if an item upon which Zakat al-Fitr is due is purchased before Shawwal begins, while the option period is still active?

Primary text

If a slave, upon whom Fitr is due, is purchased, the Fitr obligation for the beginning of Shawwal falls upon the buyer, even if the purchase occurred during the option period, because ownership was vested in him. Under the alternative view, the obligation rests upon the seller because he owned the slave during the period in which the obligation arose, i.e., during the option period.