Musannaf Ibn Abi Shayba 28:76

Waki’ narrated to us, he said: Al-Mundhir ibn Tha’labah al-‘Abdi narrated to us, from ‘Ali ibn Ahmar al-‘Askari (or from Ibn Buraydah, Al-Mundhir was in doubt), he said: Some people from the Muhajirun said to ‘Umar: "When we see the enemy and we see that they have covered their weapons with silk, we feel awe because of that." ‘Umar said: "You, if you wish, then cover your weapons with silk and brocade."