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

Sayyidna Harun (علیہ السلام) was three or four years senior to Sayyidna Musa علیہ السلام and died three years before the latter. When Sayyidna Musa (علیہ السلام) petitioned to Allah Ta` ala for his appointment as Wazir he was in Egypt, and there he received, through an angel, information about his elevation to the status of a prophet and his appointment as an assistant to Sayyidna Musa (علیہ السلام) . He was also instructed to receive Sayyidna Musa (علیہ السلام) outside Egypt when he arrived there in pursuance of his mission to persuade the Pharaoh to accept the true faith. This he did.