Musnad Abu Ya'la al-Mawsili 41:6

Amr al-Naqid narrated to us, Sufyan narrated to us, from al-Zuhri, from Talha ibn Abdullah ibn Awf, from Sa'id ibn Zayd, from the Prophet (may Allah bless him and grant him peace), who said: "Whoever usurps a span of land, it will be tied around his neck from seven earths." "And whoever is killed while defending his property, he is a martyr."