Surah Ar-Ra'd (The Thunder), Verse 7

وَیَقُوْلُ الَّذِیْنَ كَفَرُوْا لَوْلَاۤ اُنْزِلَ عَلَیْهِ اٰیَةٌ مِّنْ رَّبِّهٖ اِنَّمَاۤ اَنْتَ مُنْذِرٌ وَّلِكُلِّ قَوْمٍ هَادٍ 

Wa yaqoolul lazeena kafaroo law laaa unzila 'alaihi Aayatum mir Rabbih; innamaaa anta munzirunw wa likulli qawmin haad

“And the Unbelievers say: "Why is not a sign sent down to him from his Lord?" But thou art truly a warner, and to every people a guide.”

Quran 13:7 (Yusuf Ali Translation)