The Hand of Musa turning White without any Disease

This is the second sign of Musa. That is Allah has commanded him to place his hand into the opening of his garment, as is clearly stated in another Ayah. It mentioned here merely as a passing reference, saying:

وَاضْمُمْ يَدَكَ إِلَى جَنَاحِكَ

اذْهَبْ إِلَىٰ فِرْ‌عَوْنَ (Go to the Pharaoh - 20:24). Having suitably armed him with two great miracles, Allah Ta` ala commanded Sayyidna Musa (علیہ السلام) to proceed to Egypt and invite the Pharaoh to accept the true faith because he had exceeded all bounds in his tyranny and misdeeds.