Musnad Ahmad 33:140

Hashim narrated to us, he said: Al-A’mash informed us, from Abu Sufyan, from Jabir ibn Abdullah, he said: Ubayy ibn Ka’b was struck by an arrow on the day of Uhud, and it hit his median cubital vein (akhal). The Prophet, peace and blessings of Allah be upon him, ordered that he be cauterized on his median cubital vein.