Musannaf Ibn Abi Shayba 37:163

Khalid ibn Makhlad narrated to us, he said: Ali ibn Salih narrated to us, from his father, from Sa’id ibn ‘Amr, from Abu Hakim, the freed slave of Muhammad ibn Usama, from the Prophet, peace and blessings of Allah be upon him, that he said: "How will you be when neither a dinar nor a dirham is left for you?" They said: "And when will that be?" He said: "When you break the covenant, Allah will harden the hearts of the enemy against you, and they will withhold from you."