Musnad Ahmad 31:429

Hajjaj and Abu al-Nadr narrated to us, they said: Shareek narrated to us, from Abdullah ibn Isam Abu Alwan, he said: I heard Abu Sa’id al-Khudri saying: The Messenger of Allah, peace and blessings of Allah be upon him, said: "It is not lawful for anyone who believes in Allah and the Last Day to untie the *sirar* (the binding/knot) of a she-camel without the permission of its owners, for it is their seal upon it. So if you are in a wasteland and you see a *watb* (skin for milk), or a *rawiyah* (water skin), or a *siqa* (skin) of milk, then call out to the owners of the camels three times. If they give you to drink, then drink; otherwise, do not, even if you are starving." Abu al-Nadr said: "And if you have no food, then let two men among you hold it, then drink."