Buraydah (radiallahu anhu) says, "Najaashi sent two simple black coloured socks as a gift to Sayyidina Rasulullah sallallahu alaihe wasallam. He wore these and made mash over them after performing wudu". (ES)
English reference (ES): Book 9, Hadith 69 (ES)
Arabic reference (ES): Book 10, Hadith 73 (ES)