According to one classification, fanāʾ (annihilation in God) and its opposite, baqāʾ (subsistence in God), represent the final stage of the Sufi (taṣawwuf) life. According to the Sufis, when a person completes their Sufi training and attains moral perfection, their inner world becomes so overwhelmed with spiritual ecstasy that their consciousness is entirely filled with the thought of Allah. With the end of this state, the state of baqāʾ begins.
There are also those who consider the terms fanāʾ-baqāʾ synonymous with other terms expressing similar states, such as sakr-ṣaḥw (spiritual intoxication-sobriety) and ghayba-ḥuḍūr (absence-presence). Some Sufis, because they could not free themselves from the spiritual intoxication of the state of fanāʾ, established the following rule: A Sufi who does not pass through the state of fanāʾ and reach the normal conditions of the state of baqāʾ cannot become a murshid (spiritual guide), that is, cannot guide others on the Sufi path.
The station (maqām) of fanāʾ-baqāʾ is among the most delicate points in the psychology of Sufism (taṣawwuf). Critics of the subject have interpreted these experiences as ḥulūliyya (the indwelling of Allah in a person) or ittiḥādiyya (the union of a person with Allah). However, the Sufis have insisted that fanāʾ-baqāʾ has no connection with such heretical and deviant paths.
Fanāʾ-baqāʾ is closely related to the state of tawhid (the oneness of God).