Should we refrain from treating children who have incurable diseases?
Question

                Some illnesses lead the patient to be definitely mentally retarded and may even leave him with problems for the rest of his life. For example: the illnesses of the brain and nervous system. The patient of such an illness may be inside the womb, and medical examinations may show that this child will be born with a mental illness, which will make him and his parents suffer as long as he lives. 

There is a recognized idea implemented in the west that such a child should not be properly treated. Meaning to give him a chance to die as if he becomes well he will remain mentally retarded. If the patient is a fetus, then they perform an abortion so that he is stillborn. Parents sometimes even ask for this themselves; claiming that they do not want him to suffer. What is the ruling on this?.
Praise be to Allah.
    One of the five essentials which the texts of the Qur’aan and 
    Sunnah indicate must be preserved, and on which the ummah is unanimously 
    agreed, is preservation of human life, which comes second only to 
    preservation of religious commitment, whether the individual is a foetus 
    into whom the soul has been breathed or he has been given birth to, and 
    whether he is free of diseases, problems and deformities or he is afflicted 
    in some sense, and whether there is the hope that he may be healed or there 
    is no such hope, on the basis of the usual means and on the basis of 
    clinical tests. So it is not permissible to transgress against him by 
    aborting him if he is a foetus into which the soul has been breathed or by 
    giving him medicines that will cause him to die or to destroy him, so as to 
    spare him pain and suffering, or to relieve his guardian (of this burden) 
    or  so as to rid society of those who have mental and physical handicaps or 
    who are deformed, or for any other reason that may motivate people to get 
    rid of them, because of the general meaning of the words of Allaah 
    (interpretation of the meaning):  

    “And do not kill anyone whose killing Allaah has 
    forbidden, except for a just cause”

    [al-Isra’ 17:33]

    And it was proven that the Prophet  (peace and blessings 
    of Allaah be upon him) said: “It is not permissible to shed the blood of a 
    Muslim (by passing a verdict of execution) except in three cases: a life for 
    a life, an adulterer who is married (or previously married), and one who 
    leaves his religion and separates from the jamaa’ah.” Narrated by 
    al-Bukhaari and Muslim. They should seek reward for that and not complain 
    about the frequency of the sick person’s visits to the doctor, or feel 
    distressed because of the length of treatment, and they should not despair 
    of good consequences, because all matters are in the hand of Allaah and He 
    directs them as He wills. So they should not lose patience if the cure is 
    not easy to find and death is expected. How often has a sick person been 
    faced with a difficult-to-treat illness and his condition has deteriorated, 
    then Allaah bestowed healing upon him. And how often has a sick person been 
    diagnosed with a sickness and has taken the medicine and hoped for a cure, 
    then he died despite the great care of those who were treating him. Medical 
    skills and experience should not make doctors regard what they think is 
    going to happen as being something definite and inevitable, and they should 
    not regard their expectations as reality. How often have speculations proven 
    false and expectations proven wrong. They should realize that even though we 
    are enjoined to implement the means, healing comes only from Allaah Who has 
    created the means. Knowledge of people’s lifespans belongs only to Him, and 
    no one knows them except Him. The authorities should prepare facilities for 
    treatment, and supply doctors, equipment, hospitals and so on. Everyone is a 
    shepherd and is responsible for his flock, each in his own field according 
    to the knowledge, physical strength and financial ability that Allaah has 
    given him, as the Messenger of Allaah  (peace and blessings of Allaah be 
    upon him) told us. They should all do their jobs well, for Allaah has 
    decreed proficiency in all things and He loves those who do well. 

    They do not have the right to withhold treatment or be 
    careless about it, by neglecting to implement the means of healing. 

    The presence of the mentally and physically handicapped, and 
    the chronically ill, is good for people, and it is a reminder and 
    exhortation, and a great sign of the wisdom of Allaah and His ability to do 
    whatever He wills, and the greatness of His blessing to those who are free 
    of these sicknesses, so that they show gratitude to him and obey Him. 

    And Allaah is the Source of strength. May Allaah send 
    blessings and peace upon our Prophet Muhammad and his family and companions. 
    End quote. 

    Standing Committee for Academic Research and Issuing Fatwas 

    Shaykh ‘Abd al-‘Azeez ibn ‘Abd-Allaah b nbaaz, Shaykh ‘Abd 
    al-Razzaaq ‘Afeefi, Shaykh ‘Abd-Allaah ibn Ghadyaan, Shaykh ‘Abd-Allaah ibn 
    Qa’ood 

    Fataawa al-Lajnah al-Daa’imah li’l-Buhooth al-‘Ilmiyyah 
    wa’l-Ifta (24/389).