Zayd bin Wahb said that a letter from Umar bin al-Khattab (may Allah be pleased with him) came to them while they were engaged in one of the military expeditions: "News has reached me that you eat cheese; so see what of it is lawful and what is unlawful. And you wear furs; so distinguish the properly slaughtered from the carrion."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19390