Musnad Abu Ya'la al-Mawsili 153:131

Ishaq narrated to us, Abd al-Razzaq narrated to us, Ma'mar narrated to us, from al-Zuhri, from Salim, from Ibn Umar, that the Prophet, peace and blessings of Allah be upon him, saw a white shirt on Umar and said: "Is your shirt new or washed?" He said: "I think he said 'washed'." The Prophet, peace and blessings of Allah be upon him, said: "Wear it new, live praiseworthy, and die a martyr."