Yahya related to me from Malik that he had heard that Said ibnal-Musayyab and Sulayman ibn Yasar said, "The head wound of the slavein which the bone is bared is a twentieth of his price." (FR)
USC-MSA web (English) reference: Book 43, Hadith 8 (FR)
Arabic reference (FR): Book 43, Hadith 1580 (FR)