Suwayd bin Ghafalah (may Allah have mercy on him) said: Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) delivered a sermon at al-Jabiyah, saying that the Prophet (peace and blessings be upon him) "permitted wearing silk only up to the measure of two, three or four fingers."
(b) Abu Uthman (may Allah have mercy on him) narrates from Sayyiduna Umar (may Allah be pleased with him) that he used to forbid wearing silk, but (pointing, he said:) the measure of two, three or four fingers is permitted, and the Prophet (peace and blessings be upon him) too "used to forbid more than that."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الخوف / 6083