The fly was stubborn. It settled on his face once more. He tried to kill it, failed, got angry. He then asked Dahhak, a scholar who was present:
“Why has Allah (swt) created this annoying insect? Doesn’t it seem useless?”
Dahhak replied: “It was created to show tyrants like you how impotent they really are; that they don’t even have the power to dispose of a fly.
You may hold sway over human beings, yet a feeble little insect refuses to obey you. It settles on dirt, then comes and lights on the faces of those who imagine they are Allah (swt).
If it could express itself in words, it would say: “You are a nonentity. Do not forget that you are nothing. You may conquer the world, but you cannot conquer me. If Allah (swt) wills, He can kill you, as He killed Nimrod, with a miserable little fly.”
Taken from the Irshad (Wisdom of a Sufi Master) By Sheikh Muzaffer Ozak Al-Jerrahi, Page 365-366