Umar bin Muhammad bin Zayd bin Abdullah bin Umar narrates from his father that Abdullah bin Umar (may Allah be pleased with them both) made a contract of manumission with one of his slaves, named Sharaf, for 40,000. He went to Kufah and worked there with donkeys, and he earned and paid 15,000. Then a man came to him and said: Are you mad? Abdullah bin Umar (may Allah be pleased with them both) buys slaves and frees them, while you have put yourself through torment. Go to him and tell him: I have become unable to pay. So he came, bringing his document with him, and said: O Abu Abd al-Rahman! I have become unable to pay; this is my document, cancel it. Abdullah bin Umar (may Allah be pleased with them both) said: If you wish, erase it yourself; I will not erase it. So he erased it, and the eyes of Ibn Umar (may Allah be pleased with them both) filled with tears, and he said: Go, you are free. He said: May Allah grant you good, be kind to my sons as well. He said: They both are free too. He said: (Free) my mother and the mother of my children as well. He said: They both are free too. So he freed all five of them while sitting in one place.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21756