قُلْ إِنِّي عَلَى بَيِّنَةٍ مِّن رَّبِّيSay:"I am on clear proof from my Lord..."means:I have a clear understanding of the Law of Allah that He has revealed to me,وَكَذَّبْتُم بِهِbut you deny it.meaning, but you disbelieve in the truth that came to me from Allah.مَا عِندِي مَا تَسْتَعْجِلُونَ بِهِI do not have what you are hastily seeking,meaning, the torment,إِنِ الْحُكْمُ إِلاَّ لِلّهِThe decision is only for Allah,for the ruling of this is with Allah. If He wills, He will punish you soon in response to your wish! If He wills, He will give you respite, out of His great wisdom.This is why Allah said,يَقُصُّ الْحَقَّ وَهُوَ خَيْرُ الْفَاصِلِينَHe declares the truth, and He is the best of judges.and the best in reckoning between His servants.Allah's statement