Abu Uthman (may Allah have mercy on him) said: Sayyiduna Utbah bin Farqad (may Allah be pleased with him) sent fine khabis (a sweet) from Azerbaijan to Sayyiduna Umar (may Allah be pleased with him) with him (Abu Uthman) and with a slave of his; he had it prepared in baskets covered with felt. When he reached Sayyiduna Umar (may Allah be pleased with him), he uncovered the sweet. Sayyiduna Umar (may Allah be pleased with him) asked: Do the Muslims in their homes eat their fill of this? The messenger answered no. Sayyiduna Umar (may Allah be pleased with him) said: I do not want it. And he wrote to Sayyiduna Utbah (may Allah be pleased with him): This is not from your earnings, nor from the earnings of your father or your mother; so feed the Muslims around you, in their homes, their fill of what you eat your fill of in your own home. Then he said: Wear the waist-wrap, the upper wrap and sandals; take off trousers and leather socks; shoot at targets; leave the stirrups and leap onto your mounts; hold fast to the ways of Ma'add and the Arabs; abandon luxury and the dress of the non-Arabs; and beware of wearing silk, for the Messenger of Allah (peace and blessings be upon him) forbade us from wearing silk: "Only the width of two fingers, the middle finger and the index finger, is permitted."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20412