A Clarification of Doubts Regarding Waḥdah al-Wujūd
An excellent discussion by Ibn Abū al-ʿIzz al-Ḥanafī concerning the outcomes and branches of such a pantheistic belief. He also shows which sects from amongst Islām have unfortunately adopted this evil creed.
For verily the affirmation of a thing in an abstract sense from all of the Attributes means one cannot picture it existing outside of that. And the mind will only be left thinking that it does not exist, and that is the most extreme form of taʿtīl (denial).
Al Allāmah Ibn Abīl 'Izz al-Hanafī said:
"So verily the deniers of Allāh's Attributes enter the denial of the Attributes [into] the naming of Tawḥīd, such as Jahm Ibn Ṣafwān  and his followers. For verily they say, "Affirming the Attributes necessitates that Al Wājib  is numerous." And this statement is known by necessity to be corrupt. For verily the affirmation of a thing in an abstract sense from all of the Attributes means one cannot picture it existing outside of that. And the mind will only be left thinking that it does not exist, and that is the most extreme form of ta'teel (denial). And this statement has led people to statements of Allāh being everywhere and in everything. And this is worse than the disbelief of the Christians. For verily the Christians specified it to the Messiah (Jesus), but these people use it universally on all of the creation.
And from the implications of this kind of Tawḥīd: is the belief that Firʿawn and his people completed Īmān, knowing Allāh on the reality.
And from its implications: is that the worshippers of idols are on truth and reward, and verily they only worship Allāh and not other than Him.
And from its implications: is that there is no difference between forbiddance, and permissibility, between the mother, and the sister, and the strange woman. And there is no difference between water and intoxicants (khamr), and adultery and marriage. And it implies that everything i from one source. No, rather He is that one source.
And from its implications: is that the prophets were oppressive to their nations.
And Allāh is far above what they say, a great Highness!!" [End of Ibn Abī al-ʿIzz's words]
 This is a brief discussion on the deviated concept of Wahdatul Wujood (the oneness of existence) by the great scholar Ibn Abī al-ʿIzz al-Hanafī. It is taken from Sharḥul ʿAqīdahtut Tahaawiyyah (p.78-79). The page references are to Shaykh al Albānī's authentication of the book. He is Abū Muharraz Jahm Ibn Ṣafwān as-Samarkandee, the misguided innovator.
 The reason the Imām Ibn Abī al-ʿIzz used the term al-Wājib when quoting the Jahmees is because of their usage of the terms "Wājib al-Wujūd", and "Mumkin al-Wujūd" etc... They used to use these terms to somehow try to justify the pantheistic concept of Wahdat al-Wujūd.