Musannaf Ibn Abi Shayba 5:433

Waki’ narrated to us, from ‘Abd al-‘Aziz ibn ‘Abd Allah, from Abu Sakhr, from Kaysan ibn Abi Sa’id al-Maqburi, who said: I came to ‘Umar with the Zakat of my wealth, [which was] two hundred dirhams, while I was a *mukātab* (a slave under a contract of manumission). He said, "Have you been emancipated?" I said, "Yes." He said, "Go and distribute it."