Musnad Ahmad 30:2492

Yahya narrated to us, from Ibn Abi Dhi'b, who said: Sa'id narrated to us, from Abu Hurairah, from the Prophet, peace and blessings of Allah be upon him, who said: "A time will surely come upon the people when a person will not care about the wealth he acquires, whether it is from a lawful source or an unlawful one."