The Prophet ﷺ allowed ʿAbdur-Rahman bin ʿAuf and Az-Zubair to wear silken shirts because they had a skin disease causing itching.
أَنَّ النَّبِيَّ ﷺ رَخَّصَ لِعَبْدِ الرَّحْمَنِ بْنِ عَوْفٍ وَالزُّبَيْرِ فِي قَمِيصٍ مِنْ حَرِيرٍ مِنْ حِكَّةٍ كَانَتْ بِهِمَا