Imam Al-Nawawi’s Riyad-us-Saliheen
Lawfulness to wear Silk in case one is suffering from an Itch
810. Anas (May Allah be pleased with him) reported: Messenger of Allah (sallallaahu alayhi wa sallam) permitted Zubair and `Abdur-Rahman bin `Auf (May Allah be pleased with them) to wear silk because they were suffering from an itch.
[Al-Bukhari and Muslim].