Musnad Abu Ya'la al-Mawsili 248:21

Abu Bakr ibn Abi Shaybah narrated to us, Hatim ibn Isma'il narrated to us, from al-Muhajir ibn Mismar, from Amir ibn Sa'd, from Jabir ibn Samurah, who said: I heard the Prophet, peace and blessings of Allah be upon him, saying: "I am the forerunner at the Hawd (the Cistern)."