Musannaf Ibn Abi Shayba 34:297

Waki’ narrated to us, from Abu Shabib, from Ikrimah, from Ibn Abbas, that Umar had a *kitabah* (contract of manumission) with a slave of his who was called Abu Umayyah. He came to him with his installment when it became due. Ikrimah said: "It was the first installment paid in Islam."