"Are you the ones who create it, or are We the creators?" [This is posed] as an interrogative, meaning: You are not the ones who create it.
﴿أَأَنْتُمْ تَخْلُقُونَهُ أَمْ نَحْنُ الْخَالِقُونَ﴾ على الِاسْتِفْهَام أَي: لَسْتُم الَّذين تخلقونه (ل ٣٥١)