Sahih al-Bukhari, Volume 7, Book 72, Hadith 730 (USC-MSA) ⓘ
Narrated Anas: The Prophet allowed Az-Zubair and `Abdur-Rahman to wear silk because they were suffering from an itch.
حَدَّثَنِي مُحَمَّدٌ، أَخْبَرَنَا وَكِيعٌ، أَخْبَرَنَا شُعْبَةُ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، قَالَ رَخَّصَ النَّبِيُّ صلى الله عليه وسلم لِلزُّبَيْرِ وَعَبْدِ الرَّحْمَنِ فِي لُبْسِ الْحَرِيرِ لِحِكَّةٍ بِهِمَا.
also referenced under: Book 77, Hadith 56 (In-Book) & Hadith 5839 (DarusSalam)