The sentence for which al-Hallaj is remembered is two words long. Ana al-haqq: I am the Truth. Al-Haqq is one of the names of God, so the utterance can be heard as a claim to be God, and it was heard that way by people with the power to act on it.
Sufi tradition has always read it otherwise, and the reading depends on a technical doctrine. In the state called fana, annihilation, the self that would ordinarily speak is not present; what speaks through the mystic is the only thing that remains. On that account the words are not a claim about a man but a report of an absence, and the correct response to them is not prosecution but silence. The alternative reading, pressed by his accusers, is hulul, indwelling: that God had taken up residence in a particular human body, which for Muslim theology is the Christian error precisely.
The dispute is not merely about one man's vocabulary. Behind it lies a genuine disagreement about how far the experience of union may be spoken about at all. The tradition of his teacher Junayd held that such states must be kept inside the circle, expressed in coded language, and followed by a return to ordinary sober duty. Al-Hallaj refused that discipline. He preached in the markets of Baghdad, in plain Arabic, to whoever was there, and the record suggests he understood exactly what the risk of doing so was.