Yahya bin Abd al-Rahman bin Hatib (may Allah have mercy on him) said: Al-Zubayr bin al-Awwam (may Allah be pleased with him) came to Khaybar and saw some bright young men, and their elegance pleased him. He asked about them and was told: They are freedmen of Rafi' bin Khadij (may Allah be pleased with him); their mother is a free woman, a freedwoman of Rafi' bin Khadij (may Allah be pleased with him), and their father is a slave of the tribe of Ashja'. So al-Zubayr (may Allah be pleased with him) bought their father and freed him, then said to the young men: "Trace your affiliation to me, for you are my freedmen." Rafi' (may Allah be pleased with him) said: "Rather, they are my freedmen; they were born while their mother was free and their father was a slave." The two of them brought the dispute to Sayyiduna Uthman (may Allah be pleased with him), and he judged in favour of al-Zubayr (may Allah be pleased with him).
This is what is well known from Uthman (may Allah be pleased with him); and something contrary to it has been narrated from al-Zuhri from Uthman (may Allah be pleased with him) with a broken (munqati') chain.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الولاء / 21520