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  

As above. Narrated Anas: ʿAbdur Rahman bin ʿAuf and Az-Zubair complained to the Prophet, i.e. about the lice (that caused itching) so he allowed them to wear silken clothes. I saw them wearing such clothes in a holy battle.  

أَنَّ عَبْدَ الرَّحْمَنِ بْنَ عَوْفٍ وَالزُّبَيْرَ شَكَوَا إِلَى النَّبِيِّ ﷺ يَعْنِي الْقَمْلَ فَأَرْخَصَ لَهُمَا فِي الْحَرِيرِ فَرَأَيْتُهُ عَلَيْهِمَا فِي غَزَاةٍ  

The Prophet ﷺ allowed ʿAbdur-Rahman bin ʿAuf and Az-Zubair bin Al-ʿAwwam to wear silk.  

رَخَّصَ النَّبِيُّ ﷺ لِعَبْدِ الرَّحْمَنِ بْنِ عَوْفٍ وَالزُّبَيْرِ بْنِ الْعَوَّامِ فِي حَرِيرٍ  

(Wearing of silk) was allowed to them (i.e. ʿAbdurRahman and Az-Zubair) because of the itching they suffered from.  

عَنْ أَنَسٍ رَخَّصَ أَوْ رُخِّصَ لِحِكَّةٍ بِهِمَا