Hisham bin Urwah narrated from his father that al-Zubayr and Rafi' bin Khadij (may Allah be pleased with them both) brought a dispute before Sayyiduna Uthman (may Allah be pleased with him): a freedwoman of Rafi' bin Khadij (may Allah be pleased with him) was married to a slave, and she had children by that slave; then al-Zubayr (may Allah be pleased with him) bought the slave and freed him. Sayyiduna Uthman (may Allah be pleased with him) gave the judgement of wala in favour of al-Zubayr (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الولاء / 21518