Musnad Ahmad 33:409

Rawh narrated to us, Zakariya—meaning Ibn Ishaq—narrated to us, he said: I heard Abu al-Zubayr, he said: I heard Jabir ibn Abdullah saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "If one of you shrouds his brother, let him improve his shroud if he is able."