Sahih Muslim Book 24, Hadith Number 5168.

Chapter : It is permissible for a man to wear silk because of itch or some other reason.

Anas b. Malik reported to them (his companions) that Allah’s Messenger (may peace be upon him) had granted concession to Abd al-Rahman b. *Anf and Zubair b. ‘Awwam for the wearing of a silk shirt during the journey and because of itch which they both had or any other disease from which both of them had been suffering.