What do the words hulool (incarnation) and ittihaad (union with the divine) mean?
Question

                When I read books about belief (‘aqeedah), I often come across refutations of those who believe in ittihaad (union with the divine), refutations of those who believe in wahdat al-wujood (“unity of being”), and so on. What is meant by hulool (incarnation) and ittihaad (union with the divine)?
Praise be to Allah.
    Hulool 
    (incarnation) and ittihaad (union with the divine) – which includes the term 
    wahdat al-wujood (“unity of being”): 

    These two 
    terms are often mentioned in books on beliefs (‘aqeedah). They are esoteric 
    and Sufi terms, and these concepts are also frequently mentioned in the 
    books of false religions such as those of the Brahmins, Buddhists and 
    others. 

    1.
    
    Hulool (incarnation)

    (a)

    What this word 
    means in general terminology is when one of two things is absorbed into or 
    incarnated into another. 

    This is 
    complete mixing. 

    Al-Jarjaani 
    (may Allah have mercy on him) said: 

    Complete 
    hulool is the union of two bodies in such a way that pointing to one is also 
    pointing to the other, such as the juice in an orange. 

    Incomplete 
    hulool is when one of the two entities acts as a vessel containing the 
    other, such as water in a jug. 

    At-Ta‘reefaat, 
    p. 92. 

    This is what 
    is meant by hulool: affirmation of two entities, one of which is present in 
    the other. 

    What is meant 
    by this word as used by Sufis and others is the incarnation or presence of 
    Allah – may He be glorified and exalted – in His creation or in some of His 
    creation. 

    (b)

    Types of 
    hulool 

    Hulool may be 
    divided into two types: 

    i.
    
    General hulool, which is the belief that Allah, may He be exalted, is 
    present in all things.

    But this 
    hulool is similar to the idea of the incarnation of the divine (i.e., the 
    Creator God) in the human (i.e., the created being), whilst affirming that 
    the two entities are distinct and separate; in other words, He is not 
    unified with the one in whom He is present, rather He is everywhere yet 
    separate. Thus this is confirmation of two separate entities. 

    This is the 
    view of the Jahamis and their ilk. 

    ii.
    
    Specific hulool, which is the belief that Allah – may He be glorified and 
    exalted – is present in some of His creation, whilst believing that there is 
    a Creator and a created being.

    This is like 
    the belief of some of the Christian sects, that divinity – meaning Allah, 
    may He be glorified and exalted – is incarnated in humanity – meaning ‘Eesa 
    (Jesus, peace be upon him) – and that ‘Eesa (peace be upon him) has two 
    natures: the divine nature when he was speaking words of revelation, and a 
    human nature when he was crucified (according to their belief). 

    This is also 
    similar to the belief of some of the extreme Raafidis, such as the Nusayris, 
    who believe that Allah – may He be glorified and exalted – was incarnated in 
    ‘Ali ibn Abi Taalib, who was God (according to their belief); thus divinity 
    was incarnated in him. This is one of their basic beliefs. 

    2.
    
    Ittihaad (union with the divine)

    (a)

    What is meant 
    by ittihaad is that two things are one thing. 

    Al-Jarjaani 
    (may Allah have mercy on him) said: 

    Ittihaad means 
    the mixing of two things until they become one thing. 

    At-Ta‘reefaat, 
    p. 9 

    (b)

    what is meant, 
    according to those who believe in this notion, is that Allah – may He be 
    glorified and exalted – becomes one with His creation or with some of His 
    creation, in the sense that all created beings or some of them are the exact 
    essence of Allah, may He be exalted. 

    (c)

    Types of 
    ittihaad: 

    i.
    
    Ittihaad in a general sense – which is also called wahdat al-wujood (“unity 
    of being”). This is the belief that everything that exists is God Himself. 
    In other words, the Creator is one with all of His creation. This is the 
    meaning of wahdat al-wujood; those who believe in it are called 
    al-ittihaadiyyah or ahl wahdat al-wujood, such as Ibn al-Faarid, Ibn ‘Arabi 
    and others.

    ii.
    
    Ittihaad in a specific sense, which is the belief that Allah, may He be 
    glorified and exalted, became one with some created beings but not others.

    Those who 
    believe in this exclude from it the idea of His being one with filthy and 
    abhorrent things; they say that He became one with the Prophets, the 
    righteous, the philosophers or others, and thus they became the exact 
    essence of Allah, may He be glorified and exalted.

    This is like 
    the view of some Christian sects who believe that divinity became one with 
    humanity, and they became one thing. This is unlike those who believe in 
    incarnation, who believe that he (i.e., Christ) has two natures, divine and 
    human.

    Those who 
    believe in ittihaad say one nature, and those who believe in hulool say 
    two. 

    (d)

    The difference 
    between hulool and ittihaad 

    The difference 
    between them may be summed up as follows: 

    i.
    
    Hulool affirms two entities, unlike ittihaad which affirms one entity.

    ii.
    
    Hulool accepts that they are separable, whereas ittihaad does not accept 
    that.

    (e)

    Examples that 
    explain the difference between hulool and ittihaad: 

    There are many 
    such examples, including the following: 

    If you put 
    sugar into water without stirring it, this is hulool, because they are still 
    two separate entities. But if you stir it until it is absorbed by the water, 
    then they become one, because they cannot be separated again. 

    But if you put 
    something different into the water, such as pebbles, then this is called 
    hulool, not ittihaad, because the pebbles are one thing and the water is 
    something else, and they can be separated. 

    (f)

    Ruling on 
    which of these two beliefs is worse 

    There is no 
    doubt that believing in hulool or ittihaad is one of the greatest kinds of 
    disbelief and heresy – Allah forbid. 

    But ittihaad 
    is worse than hulool, because it is belief in one essence, unlike hulool. 
    Moreover, the belief that He is one with everything is worse than the belief 
    that He is one with some of His creation. 

    To sum up, 
    belief in hulool and ittihaad is obviously false. Islam came to erase it 
    from people’s minds, because it is a belief that is taken from the 
    teachings, philosophies and idolatry of the Hindus, Greeks, Jews, Christians 
    and others, so it is based on fabrications and myths. 

    Taken from 
    Mustalahaat fi Kutub al-‘Aqaa’id by Shaykh Muhammad ibn Ibraaheem 
    al-Hamad, p. 42-47 

    And Allah 
    knows best.