If you are going to refute the theory then at lest try to deal with the following: 1, The problem of God being infinite yet separate from the creation. 2, The problem of God creating ex-neo. 3, The matter of whether or not existence is a predicate. 4, The fundamentality of existence etc.
Out of interest here is a reply I got from the office of Sayyid Sadiq Shirazi on this subject:
Bismillah
Salaam
The notion of wahdat al-wujood is nothing but the antithesis of Islam.
This is because there is no commonality – let alone wahdah – between the existence of creation and that of the Creator.
All the different versions of wahdat al-wujood are in contradiction with the categorical declarations made by the Almighty and the Ahl al-Bayt in this respect; and therefore all versions of the concept of wahdat al-wujood are kufr.
There are, however, some famous "Shi'a scholars" – as you put it – who believe in wahdat al-wujood; but by believing inwahdat al-wujood they are neither Shi’a nor Muslim. Amongst others, the eminent scholar Sayyid Muhammad Kadim Tabatab’ie Yazdi (the author of the authoritative work Orwat al-Wothqaa, the book that the maraje’ comment on and produce their risalah on the basis of) describes, in his Orwat al-Wothqaa, those who believe in wahdat al-wujood as kafirand consequently declares them as najis.
Some of them, in a bid to save their reputation and blend in with the Muslims, or being unawares of the essence of what they are saying, try to justify this false notion by saying there are different versions to it. But in fact the principle notion therein is totally false and rejected by Islam in no uncertain way.
It is enough that there is absolutely no mention of the notion of wahdat al-wujood, in the hadith of Ahl al-Bayt, peace be upon them, given that we have inherited a massive bulk of hadith from Ahl al-Bayt, peace be upon them. If there was any truth and credibility to this concept, we would have had some references to or mention of this notion and the imams would have elaborated upon such a pivotal issue; but – low and behold – nothing of the sort!! If this concept had any truth in it, given its significance, you would have found half of al-Kafi and two-third of Bihar filled with hadith, statements, deliberations and explanations about this matter; but nothing of the sort!! Instead we have hadith after hadith, statement after statement, and explanation after explanation dismissing, refuting, and negating such a notion as that of wahdat al-wujood altogether. The endeavour of those who try to present this notion as Islamic is similar to that of the Christians who try to convince us that the notion of trinity is a Christian concept that was taught by Jesus Christ; this is when we find no shred of evidence in the bible to support of the notion of trinity!!
Allah’s final messenger, the Prophet Muhammad, peace be upon him and his pure family, warned of people who would be known as Sufis, who would wear suf (wool) in the summer as part of their discipline to counter their desires, who would come after him who would be deviant from Islam. The twelve divinely-appointed successors or ma'soom Imams proactively rejected this notion and those who adhered to it. At different times and occasions the Imams of Ahl al-Bayt, peace be upon them, went on to explain the principle of tawheed, to establish the standing of Islam on this issue, and refute the deviant claims made by others in this respect, which were surfacing at the time. These hadith and explanations are given in various works ranging from Nahj al-Balaghah [by Imam Ali] and al-Sahifah al-Sajjaadiyyah [by Imam Sajjad] to those such as al-Tawheed by al-Saduq, al-Bihar by al-Majlisi. In addition to numerous specific hadith that we have from our Imams to refute this notion, we also have numerous references to the Islamic tawheed that refute those false notions in most of the dua's or supplications!! For example look at the Du’a of the Day of Arafah, du’a#47 of al-Sahifah al-Sajjaadiyyah, or – now that we are in the Holy Month of Rajab – study the half-a-dozen or so du’as that are reported for this month – you will find them beautiful and also amazing in addressing the qualities and attributes of the Almighty in respect of tawheed, which at the same time proactively refute and rebuff any aspect of the notion of wahdat-al-wujood!!
Following from the lead of their ma'soom imams and the Ahl al-Bayt, peace be upon them, all true Shi'a scholars have – unanimously and vehemently – rejected this ludicrous notion throughout the ages, and they, citing relevant details, describe this notion as nothing but purely the teachings of Iblis (Satan), who has sworn to deviate mankind from the true path in any way he can.
Of course this notion is not particular to our time – or to the Islamic era – but its roots can be found in old eastern (Indian) religions the idea of which reached old Persia and Greek philosophies, such as plutonic philosophies, during the pre-Islamic era. In their bid to disperse the people from around the Ahl al-Bayt, peace be upon them, the Abbasid rulers systematically commissioned translators to have these philosophies translated from Greek to Arabic and circulated amongst the Muslims. The Abbasids were quite serious about this, and they founded the massive Dar al-Hikmah for this infamous task. [The project of translating those Greek works was first started by the Umayyad's rulers for the said purpose, but the project took second priority when the Umayyad dynasty began to crumble.] Those rulers could not imagine it in their wildest dreams how far-reaching and widespread this belief would become, and flourish even amongst the so-called Shi'a scholars one thousand years later.
The notion of wahdat al-wujood is so absurd that even, for the sake of argument, if we did not have all the hadith from the Ahl al-Bayt, peace be upon them, it would have been enough – to the sound mind – the declaration made by the Almighty in this respect in the Holy Qur’an: {there is nothing like His example} (42:11).
Furthermore, the notion of wahdat al-wujood – to the sound mind – is nothing but a figment of the imagination of the human mind, no matter how elaborate and detailed this imagination may be.
There could be countless thinkers contemplating the essence of the Almighty over countless number of years, but all those careful thoughts and deliberations cannot contain or encompass the essence of the Almighty. Whatever comes to the mind of man about the essence or likeness of the Almighty, we can certainly be assured of one thing – that that is NOT the Almighty.
The knowledge and understanding of the essence of Allah cannot be contained within the mind and understanding of man. Any understanding or possible imagination man can have about the Almighty, then that would NOT be Him and it would NOT be a correct reflection of the Almighty. That is why when the Almighty describes Himself to mankind, He resorts to declaring{there is nothing like His example}.
"The notion of the existence of Allah Almighty is simply beyond the imagination of the human mind", as the hadith and supplications declare. "Anything that the human mind can possibly think of or imagine, He is not that", the hadith stresses.
This is on the aspect of knowledge and understanding of the essence of the Almighty.
On the other hand, on the issue of union or wahdat, there is absolutely no commonality between everything that is created in existence, and the Creator; let alone there being any unity or wahdat between them. This is what the Sufis and the Aarifs claim, including the likes of Mulla Sadra. Please contemplate on this second point without us presenting further discussion......
[In his book “Insan-e Kamel”, p126, Sheikh Murteza Mutahari states: “. . . and some of those who believe in ‘Irfan and wahdat al-wujood, at certain stages, declare that they are God”!!]
Furthermore, contemplate about the hadith and supplication of Imam Jawad (the tenth imam) that addresses the Almighty: "O He who is sufficient (not in need) of everything, while everything in the heavens and earth is in need of Him."
[Perhaps this is not the best translation for this beautiful and short hadith –
يا من يكفي من كل شئ و لا يكفي منه شئ ]
Also contemplate about the Qur'anic verse [I created you while you were not a thing]. (19:9)
And you will realize that in existence we have Allah, the Creator, and we have everything else, the created.
Those who believe in the notion of wahdat al-wujood have gone astray from the teachings of Islam and Ahl al-Bayt, peace be upon them, perhaps due to the training they have been subjected to. By in believing in this ludicrous notion, the Sufis, Aarifs, and whoever "Shi'a scholars" believe in wahdat al-wujood have abandoned the most basic principle and teaching of Islam, and therefore have become completely deviant from this pure and beautiful religion. For example, in his tafsir al-Mizan, Sayyid Muhammad Hussein Tabataba'ie states something that reveals how deviant they have become. In volume 1, pp28-29 (Beirut edition, 1980) under commentary of surah al-Hamd, he states, "the path to Allah is two paths; the path of the believers, which is the shorter one, and the path of the non-believers, which is the longer."
We shall make no comment on this astonishing statement of his and leave you to contemplate on it.
Was-salaam
NB. This reply has been an extremely short response to your question, and it is not an all-comprehensive refutation ofwahdat al-wujood, but it is just to give an outline and a hint at the invalidity of the notion. A comprehensive refutation ofwahdat al-wujood would be beyond the scope of such a reply.
