Hisham bin Urwah narrates from his father that Ali bin Abi Talib (may Allah be pleased with him) said: "O my sons! Do not give your daughters in marriage except to their equals (kufu', families of equal standing)." They asked: O father, who are the equals? He said: "The children of al-Zubayr bin al-Awwam."
Hadith Referenceالمعجم الكبير للطبراني / العشرة / 234