Wahdat al-Wujood according to the Ahlus sunnah Wal Jamaa is a concept explained by the mystics as when a person who is treading the path of reformation becomes so conscious of the existence and presence of Allah that he becomes oblivious to everything else. In all of the creation of Allah, he sees the greatness of Allah with the result that he becomes so overwhelmed with the greatness of Allah than the creation itself seems non-existent. This in no way negates the existence of the creation of Allah. By example, in a wresting contest between a professional wrestler and a child, the child seems non-existent. This does not negate the presence of the child. However, the overwhelming presence, strength and control of the wrestler makes one oblivious of the presence of the child.
(Ahsanul Fataawa vol. 1 pg. 554; Karachi)
Below is the summary of the explanation of Wahdat al-Wujood by Maulana Zafar Ahmad Usmani (Rahimullah Ta’ala) in the introduction of his Urdu book “Al-Qawlul Mansur fi Ibn al-Mansur” (also known as “Seerat-e-Mansur Hallaj”).
Allah Ta’ala has many qualities, one of them is wujood (existence). The wujood of Allah is compulsory (Allah is wajib al-Wujood). The wujood of Allah has no beginning and no end. The wujood of the creation of Allah is hadis (of recent occurrence) and dependent upon Allah Ta’ala in all its aspects.
Regarding the wujood of the creation, the Ulama-e-Zahir say that the wujood of the creation is mustaqil (confirmed), meaning that it is not a shadow of the existence of Allah but entirely dependent upon Allah in all its aspects. The soofia-e-kiram say that the wujood of the creation is ghair-mustaqil (unconfirmed). Indeed, the wujood of the creation is khayali (speculative). The real wujood is that of Allah alone. The entire creation is a testimony of the wujood of Allah. In other words, the existence of the creation is totally different than the existence of Allah. One can not make qiyas (analogical deduction) of Allah’s wujood with that of the creation. The existence of Allah is real and independent. Therefore, wahdat al-wujood means that Allah is one in His existence as He is one in His zaat (self/identity). It is a much deeper notion of tawheed (oneness of Allah). Wahdat as-shuhood means that the mere speculative existence of the creation testifies the independent existence of Allah.
Wujood-e-khayali (the speculative existence of the creation) is of two types:
Ghair waqi’ee (non-occurring)
The soofia say that the creation is waqi’ee (occurring) but its occurrence is limited in terms of makaan (place) and zamaan (time) and dependent upon Allah. It would be wrong to call the creation non-occurring and say that everything one sees is Allah, this is against the aqaa’id (beliefs) of the Ahle Sunnah wal Jamaah. This is where all the misunderstanding arises. In reality, the beliefs held by the soofia-e-kiram in regards to the oneness of Allah are in exact accordance with Ahle Sunnah wal Jamaah and much deeper and firm-rooted than those of the ulama-e-zahir. Once a person believes that the creation is only speculative then he will not think and believe that the benefits and harms being displayed by the creation are its creation but all harm and benefit is the creation of Allah. The creation only displays the orders of Allah. The hikmah (wisdom) of wahdat al-wujood and wahdat as-shuhood is to ingrain a deep yaqin (conviction) of Allah in the depths of the hearts. If a person has a hard time understanding this, he should stick to the basic beliefs and tenets of Islam as described by the ulama-e-zahir because these are proven from the Quran with clarity. However, one does not have the right to criticize the soofia for their beliefs just because one is unable to understand the reality of their views. One should also understand that the views of the soofia regarding wahdat al-wujood are not from the fundamentals of tassawwuf and understanding it is not a condition for a saalik (seeker of truth). Those who speak ill of the soofia should fear Allah and contemplate over the following Hadith of Rasulullah (Sallallahu Alayhi WaSallam):
إملاء الخير خير من السكوت والسكوت خير من إملاء الشر رواه البيهقى فى شعب الايمان
“Speaking what is good is better than silence and silence is better than talking evil.” (Reported by al-Bayhaqi)