Musnad Ahmad 33:971

Muhammad ibn Bishr narrated to us, Sa'id ibn Abi 'Arubah narrated to us, Qatadah narrated to us, from Sulayman ibn Qays al-Yashkuri, from Jabir ibn 'Abd Allah al-Ansari, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever encloses a piece of land with a wall, it is his."