Musannaf Ibn Abi Shayba 1:1508

Waki’ narrated to us, from Sufyan, from Habib, from Maymun ibn Abi Shabib, that ‘Umar ibn al-Khattab passed by the cistern of Mijannah and said, "Give me to drink from it." They said, "Indeed, the beasts of prey, the dogs, and the donkeys come to it." He said, "For them is what they carried in their bellies, and what remains is for us, a purifier and a drink."