Musnad Imam Shafi'i

It is narrated from Ismail bin Umayyah that Nafi’ informed him that Abdullah bin Umar (may Allah be pleased with them both) made a contract of manumission (mukataba) with his slave for thirty thousand. Then that slave came to him and said, “I am unable (to pay the amount).” Ibn Umar (may Allah be pleased with them both) said, “Then erase your contract of manumission.” He said, “I am helpless, you erase it yourself.” Nafi’ said, “I signaled to that slave to erase it because (Ibn Umar) wanted to set him free.” That slave erased the contract; he had one or two sons. Ibn Umar (may Allah be pleased with them both) said, “Separate from my slave-girl.” Nafi’ said: Later, Ibn Umar (may Allah be pleased with them both) also set his son free.