Sunan Ibn Majah Book 16, Hadith 51
“Whoever digs a well, is entitled to forty forearms' length surrounding it is as a resting place for his flocks.”
“Every division that was allocated according to (the rules of) the Ignorance days, stands as it is, and every division that was allocated according to (the rules of) Islam, stands according to the rules of Islam.”
“The land around a well (that is considered to be part of it) is the length of the well rope (in all directions).”