It is narrated from Abdullah bin Amir bin Kurayz (the narrator thinks it may be narrated from Sayyiduna Abdullah bin al-Zubayr (may Allah be pleased with him)) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever is killed defending his wealth is a martyr."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13887