Musnad Ahmad 32:920

Waki’ narrated to us, Shu’bah narrated to us, from Qatadah, from Anas, who said: "Permission was granted to Az-Zubayr ibn al-Awwam and ‘Abd ar-Rahman ibn ‘Awf to wear silk because of an itch they both had." Shu’bah said: And he said: "The Messenger of Allah, may Allah bless him and grant him peace, granted them permission."