Ibn Kathir (Abridged)
Hafiz Ibn Kathirوَقَالَ مُوسَى يَفِرْعَوْنُ إِنَّى رَسُولٌ مِّن رَّبِّ الْعَـلَمِينَ (And Musa said: "O Fir`awn! Verily, I am a Messenger from the Lord of all that exists".) meaning Musa said, `the one Who sent me is the Creator, Lord and King of all things,' حَقِيقٌ عَلَى أَن لاَ أَقُولَ عَلَى اللَّهِ إِلاَّ الْحَقَّ("Proper it is for me that I say nothing concerning Allah but the truth. ") `It is incumbent and a duty for me to convey only the Truth from Him, because of what I know of His might and power.' قَدْ جِئْتُكُمْ بِبَيِّنَةٍ مِّن رَّبِّكُمْ("Indeed I have come unto you from your Lord with a clear proof.") `I brought unequivocal evidence that Allah gave me to prove that I am conveying the truth to you,' فَأَرْسِلْ مَعِىَ بَنِى إِسْرَءِيلَ("So let the Children of Israel depart along with me.") means, release them from your slavery and subjugation. Let them worship your Lord and their Lord. They are from the offspring of an honorable Prophet, Isra'il, who is Ya`qub son of Ishaq son of Ibrahim, the Khalil (intimate friend) of Allah.
قَالَ إِن كُنتَ جِئْتَ بِـَايَةٍ فَأْتِ بِهَآ إِن كُنتَ مِنَ الصَّـدِقِينَ (Fir`awn said: "If you have come with a sign, show it forth, if you are one of those who tell the truth.") Fir`awn said, `I will not believe in what you have said nor entertain your request'. Therefore, he said, `if you have proof, then produce it for us to see, so that we know if your claim is true.'