Musnad Ahmad 32:1942

Waki’ narrated to us, Shu’bah narrated to us, from Qatadah, from Anas, who said: "A concession was granted to Az-Zubayr ibn al-Awwam and ‘Abd ar-Rahman ibn ‘Awf to wear silk—meaning—due to an ailment they both had." Shu’bah said: Or he said: "The Messenger of Allah, peace and blessings of Allah be upon him, granted them a concession."