Musannaf Ibn Abi Shayba 13:1395

Abu Bakr narrated to us, he said: Ibn Abi Za'idah narrated to us, from Ash'ath, from 'Amir, who said: The protected area (harim) of a well is forty cubits. In all of it, it is not for anyone to encroach upon him regarding his watering place or his water.