Musnad Ahmad 9:4

Sufyan narrated to us, he said: We memorized this from al-Zuhri, from Talhah ibn Abdullah ibn Awf, from Sa'id ibn Zayd ibn Amr ibn Nufayl: That the Messenger of Allah, peace and blessings of Allah be upon him, said: "Whoever is killed while defending his wealth is a martyr. And whoever usurps a span of land unjustly, it will be tied around his neck from the seven earths."