Al-Hallaj (Arabic: ابو المغيث الحسين بن منصور الحلاج, Abū 'l-Muġīth Al-Ḥusayn bin Manṣūr al-Ḥallāj) or Mansour Hallaj (c. 858 – 26 March 922) (Hijri c. 244 AH – 309 AH) was a Persian mystic, poet and teacher of Sufism.
Different Muslims, both Sunnis and Shi'is, have varying views about al-Hallaj. Some take a negative view of him, especially this statement, and others appreciate the spirit of it.
Regarding al-Hallaj, Ayatollah Motahhari says in his introduction to 'irfan:
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Now famous simply as al-Hallaj, he is one of the most controversial mystics of the Islamic world. The shathiyyat uttered by him are many, and he was accused of apostasy and claiming divinity. The jurisprudents pronounced him an apostate and he was crucified during the reign of the 'Abbasid caliph al-Muqtadir.
The 'urafa' themselves accuse him of disclosing spiritual secrets. Hafiz has this to say about him:
He said, that friend, who was raised high on the cross,
His crime was that he used to reveal secrets.
Some consider him no more than a charlatan, but the 'urafa' themselves absolve him and say that the statements of al-Hallaj and Bayazid that gave the impression of unbelief were made when they were beside themselves in the state of 'intoxication'.
Al-Hallaj is remembered by the 'urafa' as a martyr. He was executed in 309/913.
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So there are varying views.
Hussain Ibn Mansoor Al-Hallaaj was a Sufi who deviated and claimed that he is a representative of Imam Al-Mahdi (AS). He claimed many dangerous claims including claiming that he is Allah or part of Allah (SWT). He was cursed by our Shia scholars as well as as Sunni scholars. Our great scholar Shaikh Al-Mufeed wrote a book against him and his cult called Tasheeh Al-E'tiqadaat Al-Imamiyyah. His claim (Ana Al-Haqq) shows his deviation and falsehood.
Even Sunni scholars refused his false claims and complained against him to the Abbasid king Al-Moqtadir who killed him in year 309 Hijri.
His cult was called Al-Hallajiyyah and they did not pray Salah nor perform any Islamic worship. This was mentioned by Shaikh Al-Sadouq in Al-E'tiqadaat (97).