Surah Yunus (Jonah), Verse 20

وَیَقُوْلُوْنَ لَوْلَاۤ اُنْزِلَ عَلَیْهِ اٰیَةٌ مِّنْ رَّبِّهٖ فَقُلْ اِنَّمَا الْغَیْبُ لِلّٰهِ فَانْتَظِرُوْا اِنِّیْ مَعَكُمْ مِّنَ الْمُنْتَظِرِیْنَ 

Wa yaqooloona law laaa unzila 'alaihi aayatun mir Rabbihee faqul innamal ghaibu lillaahi fantaziroo innee ma'akum minal muntazireen

“They say: "Why is not a sign sent down to him from his Lord?" Say: "The Unseen is only for Allah (to know), then wait ye: I too will wait with you."”

Quran 10:20 (Yusuf Ali Translation)