Abu Uthman al-Nahdi (may Allah have mercy on him) said: A letter from Umar bin al-Khattab (may Allah be pleased with him) came to us while we were with Uqbah bin Farqad (may Allah be pleased with him) in Azerbaijan, saying that the Prophet (peace and blessings be upon him) "forbade silk, but permitted silk to the width of two fingers."
Abu Uthman said: We did not take long to understand that he meant the embroidered borders (of a garment).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4208