Musnad Abu Ya'la al-Mawsili 116:37

Ahmad narrated to us, Abu Dawud narrated to us, Hammam narrated to us, from Qatadah, from Anas, that Abd al-Rahman ibn Awf and al-Zubayr complained to the Messenger of Allah (may Allah bless him and grant him peace) about lice. So the Messenger of Allah (may Allah bless him and grant him peace) granted them a concession to wear silk shirts. Anas said: I saw both of them wearing silk shirts.