Musnad Ahmad 1017:47

Waki’ narrated to us, Dalham ibn Salih narrated to us, from a sheikh of theirs who is called Hujayr ibn ‘Abd Allah al-Kindi, from ‘Abd Allah ibn Buraydah, from his father, that the Negus gifted the Prophet, may Allah bless him and grant him peace, two black, plain leather socks. He wore them, then he performed ablution and wiped over them.