Musnad Ahmad 949:6

Aswad ibn Amir narrated to us, Sharik narrated to us, from Imran al-Nakhli, from a freed slave of Umm Salamah, who said: I was with the Prophet, peace and blessings of Allah be upon him, on a journey, and we reached a valley. He said: So I began to carry the people across or transport them. He said: The Messenger of Allah, peace and blessings of Allah be upon him, said to me: "You were nothing today but a ship," or "You are nothing but a ship." It was said to Sharik: "He is Safinah, the freed slave of Umm Salamah."