Praise be to Allah.
We ask Allah, the Exalted, to keep you firm on His religion and we advise you to educate yourself regarding religious matters and work righteous deeds as much as possible as that will assist you in remaining steadfast and calling to Allah.
As for your work in taking care of the mentally challenged man, then it is in principle allowed and it would be appropriate for us to mention some rulings concerning it at this time.
1. The basic principle concerning the ‘awrah (generally the private regions which are not to be seen by others) of the handicapped is that it is impermissible to look at it or touch it without a barrier. Therefore, while cleaning his private parts, you should cover them and not look at them and clean them using something like gloves. A further benefit of the gloves would be that they protect the hands from becoming tainted with impurities.
The scholars of the Permanent Committee were asked: My father was granted three sons who were all handicapped and mentally challenged, and this is a favour Allah bestows upon His select believing slaves, and all praise belongs to Allah, Lord of the worlds. These three are my brothers and I as I mentioned to you they are handicapped and incapable of taking care of themselves. Therefore, their mother looks after them and cares for them with regard to their food, drink and clothing. However, they have all matured, with the eldest being 25 years old, so is it permissible for my mother or myself to clean my elder brother and bathe him as he does not know how to clean his own body due to his handicap, keeping in mind that his ‘awrah may be exposed. They answered: It is permissible for you to clean these disabled individuals by bathing them and other means but while keeping the ‘awrah covered and cleaning it from behind a barrier like a cloth or something like it and while wearing something on the hand to avoid dirtying the hand with impurities. You should do everything you can to look after these challenged boys, and Allah does not allow the rewards of those who do well be squandered.” End quote
Sh. ‘Abd al-‘Aziz ibn Baz, Sh. ‘Abd al-‘Aziz aal ash-Sheikh, Sh. ‘Abdullah ibn Ghudayyan, Sh. Salih al-Fauzan and Sh. Bakr Abu Zayd. Verdicts of the Permanent Committee (4/425-426)
2. The mentally challenged who feel no lust towards women are included in the saying of Allah (which means): “or those male attendants having no physical desire”. The woman may reveal before them what she would normally reveal before her mahrams (close relatives whom she may not marry), which is what would normally be exposed such as the head, face, forearms and feet.
Ibn Qudamah (may Allah have mercy on him) said: “Men who have no physical desire due to old age, impotence, a terminal illness, castration…or a hermaphrodite with no desire for women: The ruling for them is the same as that of the mahram in terms of looking due to the saying of Allah, the Exalted (in meaning): “or those male attendants having no physical desire”. i.e. no desire for women. Ibn ‘Abbas said: He is the one who women are not shy in front of. And from him: He is the hermaphrodite who is incapable of an erection.” End quote from al-Mughni (7/462)
In al-Mawsoo’ah al Fiqhiyyah it states (3/8): “The Malikis, Shafi’ees and Hanbalis said (and it is one opinion of the Hanafis): The ruling of those men who has no desire for women is that of the mahrams in regard to looking at women; they see the places of beauty such as the hair and the forearms, and the rules for entering upon them is also like that of the mahrams due to the saying of Allah , the Exalted (in meaning): “or those male attendants having no physical desire”. End quote.
3. For your work, if you need to look at or touch his ‘awrah, then it is permissible since it is a dire need or necessity as is the case with a doctor if he needs to look at or touch the ‘awrah of a patient. In al-Mawsoo’ah al-Fiqhiyyah it states (14/19): “There is no difference among the jurists that looking at the ‘awrah of another is impermissible with the exception of a married couple each looking at the other, so it is not permissible for anyone to look at another’s ‘awrah (besides them) as long as there is no need for it such as a doctor looking at the patient and a caregiver assisting a patient in wudhu (ablution), isntinjaa (cleansing after answering the call of nature), and such things or a midwife for they are permitted to look at that part of the ‘awrah which it is necessary to look at. When necessary for the purposes of treatment or care, it is permissible as necessity makes the warned against (forbidden) permissible and (dire) need is treated as necessity.
Looking is restricted to what is necessary because what is allowed due to necessity must be well assessed/evaluated.” End quote
4. If it happens that you touch the man for the purpose of cleaning and grooming him, then we differentiate between touching ‘awrah (private part) directly and the rest of the body; touching his private part directly (no barrier) nullifies the wudhu while touching the rest of his body does not. With regard to touching his private part, the scholars of the Permanent Committee said: “Touching the private part without a barrier nullifies the wudhu whether the one touches is big or small due to what is established from the saying of the Prophet (may peace and blessings be upon him): “Whoever touches his private part, let him take wudhu.” An-Nasai, Ibn Majah and authenticated by al-Albani. Touching the private part of another is like touching one’s own private part.
Sh. ‘Abd al-‘Aziz ibn Baz, Sh. ‘Abd ar-Razzaq ‘Afifi, Sh. ‘Abdullah ibn Ghudayyan, Sh. ‘Abdullah ibn Qu’ood. Verdicts of the Permanent Committee (5/265).
As for the issue of a woman touching the body of a man and it not nullifying the wudhu, then we have explained that in detail in the answer to question 76115.
5. Finally, we see that the woman should look after those of her gender and the man should look after men. Therefore, if you could find work taking care of a woman, that would be best without doubt.
And Allah knows best.