Hadith: The Prophet (may Allah's peace and blessings be upon him) used to say: O Allah, I seek refuge in You from leucoderma, insanity, leprosy, and evil diseases

عن أنس بن مالك رضي الله عنه قال: كَانَ رَسُولُ اللهِ -صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ- يَقُولُ: «اللهم إني أعوذ بك من البَرَصِ، والجُنُونِ، والجُذَامِ، وَسَيِّئِ الأسْقَامِ».
[صحيح] - [رواه أبو داود والنسائي وأحمد]

Anas ibn Mālik (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) used to say: "O Allah, I seek refuge in You from leucoderma, insanity, leprosy, and evil diseases."
Sahih/Authentic. - [An-Nasaa’i]

Explanation

In this Hadīth the Prophet (may Allah's peace and blessings be upon him) seeks refuge in Allah from specific illnesses. However, when the Messenger of Allah (may Allah's peace and blessings be upon him) seeks refuge in Allah from them, this means that they are very dangerous and have a very bad effect. The Prophet (may Allah's peace and blessings be upon him) sought Allah's refuge from a group of particular diseases, then he asked Allah to keep him healthy and safe from all evil and bad diseases in general. This supplication includes a specific and detailed part followed by a general and comprehensive part. To clarify, the Prophet (may Allah's peace and blessings be upon him) sought refuge in Allah from leucoderma, a disease in which white spots appear on the skin, that makes people turn and run away from the one who has it. This causes man to become isolated and thus feel discontented - Allah forbids. Insanity refers to the disappearance of one's mind. The mind is the thing which makes one competent for religious assignment, and with it one worships his Lord as well as ponders and reflects on Allah's creation and holy Speech. Hence, absence of mind means that man does not exist. For this reason, the Prophet (may Allah's peace and blessings be upon him) said: "There are three (kinds of people) whose actions are not recorded: (one of them is) and the insane until his mind is back." "Leprosy" is a type of sickness that eats at one's organs until they fall off, Allah forbids. It is a contagious disease, and this is why it was mentioned in another Hadīth: "Flee from the leper as you would flee from a lion." "Evil and bad diseases are the disabilities that make one feel disdained and rejected in the society, such as cancer, blindness, paralysis, etc. This is because these types of diseases are serious and need a lot of money for treatment. They also need great patience that are only shown by those whom Allah, the Almighty, grants patience and strengthens their hearts. This Hadīth shows the greatness of Islam that protects the Muslim's religion and cares for his body.