قُل لَّوْ أَنَّ عِندِى مَا تَسْتَعْجِلُونَ بِهِۦ لَقُضِىَ ٱلْأَمْرُ بَيْنِى وَبَيْنَكُمْ ۗ وَٱللَّهُ أَعْلَمُ بِٱلظَّـٰلِمِينَ
Qul law anna 'indee maa tasta'jiloona bihee laqudiyal amru bainee wa bainakum; wallaahu a'lamu bizzaalimeen
Say, "If what you seek to hasten were in my hands, the matter between me and you would already be settled. And God knows best who the wrongdoers are."
The demand being answered here is a taunt: bring on the punishment you keep threatening us with. The reply concedes something unexpected, that if the timing were the Prophet's to set the argument would already be finished, so the delay they mock is God's forbearance rather than any man's. The closing clause then takes the verdict on who has earned punishment out of every human hand, the Messenger's included.