Musannaf Ibn Abi Shayba 13:1398

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sufyan narrated to us, from Isma’il ibn Umayyah, from al-Zuhri, from Sa’id ibn al-Musayyib, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "The protected area (harim) of a Bedouin’s well is twenty-five cubits, and the protected area of an ancient well is fifty cubits." Sa’id said: "And the protected area of a well for cultivation is three hundred cubits."