كتاب اللباس والزينة
37  
The Book of Clothes and Adornment
(2)
Chapter: The Prohibition Of Using Vessels Of Gold And Silver For Men And Women, And Gold Rings And Silk For Men, But They Are Permissible For Women. Permissibility Of Silken Borders On Garments For Men, But It Should Not Be More Than Four Fingers Wide
(2)
باب تَحْرِيمِ اسْتِعْمَالِ إِنَاءِ الذَّهَبِ وَالْفِضَّةِ عَلَى الرِّجَالِ وَالنِّسَاءِ وَخَاتَمِ الذَّهَبِ وَالْحَرِيرِ عَلَى الرَّجُلِ وَإِبَاحَتِهِ لِلنِّسَاءِ وَإِبَاحَةِ الْعَلَمِ وَنَحْوِهِ لِلرَّجُلِ مَا لَمْ يَزِدْ عَلَى أَرْبَعِ أَصَابِعَ
Sahih Muslim 2069 g

Qatada reported:

I heard Abe 'Uthman al-Nahdi as saying: There came to us a letter of 'Umar as we were in Adharba'ijan or in Syria in the company of 'Utba b. Farqad (and the letter ran thus): After (usual praise and glorification of Allah) it is stated that Allah's Messenger (ﷺ) has forbidden the use of silk btit to the extent of these two fingers, and Abu Uthman said: We at once understood by these words that he meant (silk) patterns on (the cloth).
حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، وَابْنُ، بَشَّارٍ - وَاللَّفْظُ لاِبْنِ الْمُثَنَّى - قَالاَ حَدَّثَنَا مُحَمَّدُ، بْنُ جَعْفَرٍ حَدَّثَنَا شُعْبَةُ، عَنْ قَتَادَةَ، قَالَ سَمِعْتُ أَبَا عُثْمَانَ النَّهْدِيَّ، قَالَ جَاءَنَا كِتَابُ عُمَرَ وَنَحْنُ بِأَذْرَبِيجَانَ مَعَ عُتْبَةَ بْنِ فَرْقَدٍ أَوْ بِالشَّامِ أَمَّا بَعْدُ فَإِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم نَهَى عَنِ الْحَرِيرِ إِلاَّ هَكَذَا إِصْبَعَيْنِ ‏.‏ قَالَ أَبُو عُثْمَانَ فَمَا عَتَّمْنَا أَنَّهُ يَعْنِي الأَعْلاَمَ‏.‏
Reference : Sahih Muslim 2069g
In-book reference : Book 37, Hadith 30
USC-MSA web (English) reference : Book 24, Hadith 5154
  (deprecated numbering scheme)