Musnad Ahmad 32:1049

Bahz narrated to us, and 'Affan narrated to us, they both said: Hammam narrated to us—'Affan said in his narration: He said: Qatadah narrated to us, that Anas informed him: "That al-Zubayr and 'Abd al-Rahman ibn 'Awf complained to the Prophet, peace and blessings of Allah be upon him, about lice, so they sought his permission during a military expedition of theirs, and he granted them a concession to wear silk shirts." Bahz said: Anas said: "And I saw each one of them wearing a shirt of silk."