Why Allah creates mentally disabled people
Question

Why has Allah created mentally Disabled people
Praise be to Allah.One of the basic principles of Islam is to believe in the wisdom of the Lord in what He creates and commands, and in what He wills and decrees, in the sense that He does not create anything in vain and He does not decree anything in which there is not some benefit for His slaves. So everything that exists is His will and decree. Allah says (interpretation of the meaning):
“Allah is the Creator of all things” [al-Ra’d 13:16]
 His perfect wisdom decrees that He creates opposites, so He has created angels and devils, night and day, purity and impurity, good and ugly, and He has created good and evil. He created His slaves with differences in their bodies and minds, and in their strengths. He has made some rich and some poor, some healthy and some sickly, some wise and some foolish. By His wisdom, He tests them, and He tests some by means of others, to show who will be grateful and who will be ungrateful. Allah says (interpretation of the meanings):
“Verily, We have created man from Nutfah (drops) of mixed semen (sexual discharge of man and woman), in order to try him, so We made him hearer and seer.
Verily, We showed him the way, whether he be grateful or ungrateful” [al-Insaan 76:2]
“Who has created death and life that He may test you which of you is best in deed”
[al-Mulk 67:2]
 When the sound believer sees disabled people, he recognizes the blessing that Allah has bestowed upon him, so he gives thanks for His blessing, and He asks Him for good health. He knows that Allah is Able to do all things.
 People are incapable of comprehending Allah’s wisdom. He cannot be questioned as to what He does , while they will be questioned. Glorified and exalted be He. Whatever you understand of His wisdom, believe in it, and whatever you cannot understand, say, “Allah knows best and is most wise, and we know nothing except that which You have taught us, and He is the All-Knowing, Most Wise.”