Musnad Ahmad 32:1941

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, and Hajjaj said: Shu'bah narrated to me, he said: I heard Qatadah narrating from Anas ibn Malik, he said: The Prophet (may Allah bless him and grant him peace) granted a concession—or he granted a concession—to Abd al-Rahman ibn Awf and al-Zubayr ibn al-Awwam to wear silk because of an itch that was afflicting them.