ENOfficial
Anas b. Malik transmitted it from the Messenger of Allah (ﷺ) that the Great and Glorious Allah said: Verily your people would constantly question about this and that till they would say: Well, it is Allah Who created the creation, but who created Allah?
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ عَامِرِ بْنِ زُرَارَةَ الْحَضْرَمِيُّ، حَدَّثَنَا مُحَمَّدُ بْنُ فُضَيْلٍ، عَنْ مُخْتَارِ بْنِ فُلْفُلٍ، عَنْ أَنَسِ بْنِ مَالِكٍ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ " قَالَ اللَّهُ عَزَّ وَجَلَّ إِنَّ أُمَّتَكَ لاَ يَزَالُونَ يَقُولُونَ مَا كَذَا مَا كَذَا حَتَّى يَقُولُوا هَذَا اللَّهُ خَلَقَ الْخَلْقَ فَمَنْ خَلَقَ اللَّهَ " .
sunnah.com