Musannaf Ibn Abi Shayba 13:2342

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Isra’il narrated to us, from ‘Abdullah ibn ‘Ismah, he said: I heard Abu Sa’id al-Khudri saying: It is not lawful for a man to milk the she-camel of a man that has its udder tied, except with the permission of its owner. Behold, its seal is its tie. If a group of people are in dire need, the shepherd shall call out three times. If [the owner] answers, they may drink; otherwise, two men shall hold it, and they may drink.