فَإِن أَعرَضوا فَقُل أَنذَرتُكُم صاعِقَةً مِثلَ صاعِقَةِ عادٍ وَثَمودَ

But if they turn away, then say, "I have warned you of a thunderbolt like the thunderbolt [that struck] 'Aad and Thamud.