It is narrated from Ibn Shihab (may Allah have mercy on him): The one who wipes should place one hand on top of the khuff (leather sock) and one hand beneath the khuff, then wipe.
(b) Imam Malik (may Allah have mercy on him) said: Of what I have heard regarding wiping over the khuffs, this seems the most correct to me.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1383