The Prophet of Allah ﷺ took silk and held it in his right hand, and took gold and held it in his left hand and said: both of these are prohibited to the males of my community.  

أَنَّهُ سَمِعَ عَلِيَّ بْنَ أَبِي طَالِبٍ ؓ يَقُولُ إِنَّ نَبِيَّ اللَّهِ ﷺ أَخَذَ حَرِيرًا فَجَعَلَهُ فِي يَمِينِهِ وَأَخَذَ ذَهَبًا فَجَعَلَهُ فِي شِمَالِهِ ثُمَّ قَالَ إِنَّ هَذَيْنِ حَرَامٌ عَلَى ذُكُورِ أُمَّتِي  

The word "siyara" means striped with silk.  

أَنَّهُ حَدَّثَهُ أَنَّهُ رَأَى عَلَى أُمِّ كُلْثُومٍ بِنْتِ رَسُولِ اللَّهِ ﷺ بُرْدًا سِيَرَاءَ قَالَ وَالسِّيَرَاءُ الْمُضَلَّعُ بِالْقَزِّ  

We used to take it away (i.e. silk) from boys, and leave it for girls. Mis'ar said: I asked Amr ibn Dinar about it, but he did not know it.  

مِسْعَرٌ فَسَأَلْتُ عَمْرَو بْنَ دِينَارٍ عَنْهُ فَلَمْ يَعْرِفْهُ