Musnad Abu Ya'la al-Mawsili 116:35

Ahmad narrated to us, Hajjaj ibn Muhammad narrated to us, Shu'bah narrated to me, from Qatadah, from Anas, who said: The Prophet (ﷺ) granted a concession—or a concession was granted—to Abd al-Rahman ibn Awf and al-Zubayr ibn al-Awwam to wear silk because of an itch that they had.