Special Permission to Wear Silk

Hazrat Anas bin Malik (ra) relates that the Holy Prophet (sa) permitted Hazrat Zubair bin al-Awwam (ra) to a wear a silk shirt during one battle as he was suffering from irritable skin condition.

(Sahih al-Bukhari, Kitab al-Jihad wa al-Siyar, Bab al-Harir fi al-Harb, Hadith 2919)