Sahih al-Bukhari, Book 56, Hadith 135 (In-Book) ⓘ
Narrated Anas: (Wearing of silk) was allowed to them (i.e. `AbdurRahman and Az-Zubair) because of the itching they suffered from.
حَدَّثَنِي مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا غُنْدَرٌ، حَدَّثَنَا شُعْبَةُ، سَمِعْتُ قَتَادَةَ، عَنْ أَنَسٍ، رَخَّصَ أَوْ رُخِّصَ لِحِكَّةٍ بِهِمَا.
also referenced under: Hadith 2922 (DarusSalam) & Volume 4, Book 52, Hadith 172 (USC-MSA)