Surah Al-Anbiya, ayah 38

21:38

وَيَقُولُونَ مَتَىٰ هَٰذَا ٱلۡوَعۡدُ إِن كُنتُمۡ صَٰدِقِينَ ٣٨

Wayaqūlūna matā hādhal-wa'du in kuntum sādiqīn

And they say, "When is this promise, if you should be truthful?"