Quran 21:38 from Surah Al-Anbiyaa on Divine Marvels.
وَيَقُولُونَ مَتَىٰ هَٰذَا ٱلۡوَعۡدُ إِن كُنتُمۡ صَٰدِقِينَ
English translation: And they say When (will be fulfilled) this promise if you are truthful
Transliteration: wayaquluna mata hadha al-wa'du in kuntum sadiqina