I say, and with God's success: It is sufficient for him if he wipes over the khuff (footwear) the amount of the obligatory - which is the length and width of three fingers of the hand - even if he does not spread the fingers; because spreading the fingers is a Sunnah and not an obligation in wiping, but he has contradicted the Sunnah. See: Al-Wiqayah and its explanation, p. 114, and Al-Hadiyyah Al-‘Ala’iyyah, p. 41, and God knows best.