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

His second prayer was يَسِّرْ‌ لِي أَمْرِ‌ي (make my task easy for me - 20:26). Having been granted prophethood he realized that it is not the human ability and skill or other apparent causes which make affairs easy or difficult. In reality, things become easy or difficult as Allah Ta` ala wills. In the hadith the believers have been advised to seek Allah Ta’ ala's help in their affairs with the following words:

اللَّھُمَّ الطُف بِنَافی تَیسِیرِ کُلِّ عَسِیرِ فَاِنَّ تَیسِیرَ کُلِّ عَسِیرِ عَلَیکَ یَسِیرُ