Musannaf Ibn Abi Shayba 13:2587

Abu Bakr narrated to us, he said: Ibn Abi Za'idah narrated to us, from Ibn 'Awn, from Muhammad, he said: A *mukātab* (an enslaved person with a contract of manumission) wanted to give his master all the wealth at once. He (the master) said: "I will not take it except in installments." So Uthman wrote for his manumission, and he (the master) took the wealth. He (Uthman) said: "I will give it to you in installments." When the man saw that, he took the wealth.