Sura 6 Al-An'am (The Cattle), ayah 109

1. وَأَقْسَمُوا بِاللَّهِ جَهْدَ أَيْمَانِهِمْ لَئِنْ جَاءَتْهُمْ آيَةٌ لَيُؤْمِنُنَّ بِهَا ۚ قُلْ إِنَّمَا الْآيَاتُ عِنْدَ اللَّهِ ۖ وَمَا يُشْعِرُكُمْ أَنَّهَا إِذَا جَاءَتْ لَا يُؤْمِنُونَ

   And they swear by Allah their strongest oaths that if a sign came to them, they would surely believe in it. Say, "The signs are only with Allah." And what will make you perceive that even if a sign came, they would not believe.

   6:109

Translation: Saheeh International