Yahya related to me from Malik from Ibn Shihab that Ubaydullah ibn Abdullah ibn Utba ibn Masud told him that Abdullah ibn Masud bought a slave-girl from his wife, Zaynab Ath Thaqafiyya. She made a condition to him, that if he bought her, she could always buy her back for the price that he paid. Abdullah ibn Masud asked Umar ibn al- Khattab about that and Umar ibn al-Khattab said, "Do not go near her while anyone has a condition concerning her over you

English translation · Muwatta Malik