Money.

Hud [11:88]

He said: "O my people! Tell me, if I have a clear evidence from my Lord, and He has given me a good sustenance from Himself (shall I corrupt it by mixing it with the unlawfully earned money). I wish not, in contradiction to you, to do that which I forbid you. I only desire reform to the best of my power. And my guidance cannot come except from Allâh, in Him I trust and unto Him I repent.