The philosophy of Wahdat al-Wujud was first ever prevailed by Husayn ibn Ali in his book Mirat-ul-Arifeen which he wrote in response to the question of his son Zayn al-Abidin about the explanation of Surah Al-Fatiha.
In this book, he interpreted the ideology of Wahdat al-wujud for the first time in the most comprehensive way.
God's 'names' (asmāʾ) or 'attributes'(ṣifāt), on the other hand, are the relationships which can be discerned between the Essence and the cosmos.
They are known to God because he knows every object of knowledge, but they are not existent entities or ontological qualities, for this would imply plurality in the godhead.
Ibn Arabi’s doctrine of wahdat ul wujud focuses on the esoteric (batin) reality of creatures instead of exoteric (zahir) dimension of reality.It is also associated with the Hamah Ust (Persian meaning "He is the only one") philosophy in South Asia. According to this school, the reality and existence are identical which means existence is one but graded in intensity.This methodology was given a name of tashkik al-wujud and it thus explains that there is gradation of existence that stand in a vast hierarchical chain of being (marāṭib al-wujūd) from floor (farsh) to divine throne (ʿarsh), but the wujūd of each existent māhīyya is nothing but a grade of the single reality of wujūd whose source is God, the absolute being (al-wujūd al-mutlaq)."God possesses Nondelimited Being, but no delimitation prevents Him from delimitation.On the contrary, He possesses all delimitations, so He is nondelimited delimitation" On the highest level, wujūd is the absolute and nondelimited reality of God, the "Necessary Being" (wājib al-wujūd) that cannot not exist.What differentiates the wujūd of different existents is nothing but wujūd in different degrees of strength and weakness.The universe is nothing but different degrees of strengths and weaknesses of wujūd, ranging from intense degree of wujūd of arch-angelic realities, to the dim wujūd of lowly dust from which Adam was made.Ibn-e-Arabi states that " wujūd is the unknowable and inaccessible ground of everything that exists.God alone is true wujūd, while all things dwell in nonexistence, so also wujūd alone is nondelimited (muṭlaq), while everything else is constrained, confined, and constricted.In this sense, wujūd designates the Essence of God or of the Real (dhāt al-ḥaqq), the only reality that is real in every respect.On lower levels, wujūd is the underlying substance of "everything other than God" (māsiwāAllāh)—which is how Ibn Arabi and others define the "cosmos" or "universe" (al-ʿālam).