Allah, the Almighty, said:

{Everyone upon it [the earth] will perish/vanish * And there will remain the face of your Lord…} [ar-Raḥmân 55:26-27]

Annihilation⁷⁹¹ in this respect refers to the complete fading of that which is other than the Real, with respect to knowledge, then denial, then actualization. ⁷⁹² It is of three levels:

The first level is the fanâ’ (absorption) of the recognition into He Who is recognized, and this is the fanâ’ of knowledge; ⁷⁹³ the fanâ’ of the beholding into the Beheld, and this is the fanâ’ of denial; ⁷⁹⁴ and the fanâ’ of the pursuit into the actuality, and this is the fanâ’ of actualization. ⁷⁹⁵

The second level is the annihilation of the beholding of the pursuit to eliminate it, and the annihilation of the beholding of recognition to eliminate it, and the annihilation of the beholding of the beholding to eliminate it. ⁷⁹⁶

The third level is the annihilation of the beholding of fanâ’, and this is the real fanâ’ [whereby one will be] glimpsing at the lightning of reality, sailing through the ocean of union, and pursuing the trail of subsistence. ⁷⁹⁷

⁷⁹¹ The fanâ’ that is often mentioned in Sufi discourse could mean one of three things. The first is the essence of worship. The second has some noble aspects necessary for one’s devotion and others that are not virtuous in themselves and may be problematic. The third is completely blasphemous.
The first is the annihilation of one’s wills and desires and their complete conformity with and absorption into the will of Allah. This is still not an ontological merger or union of wills, because the will is the most characteristic identifier of any being; a complete union of wills means a complete union of beings. However, this annihilation of wills (fanâ’ al-irâdât) is about our will being entirely subservient to Allah’s. The Messenger of Allah (ﷺ) said:

“None of you [truly] believes until his desires are subservient to that which I have brought.” (Reported by aṭ-Ṭabarâni)

This is where the “heart wills not anything other than the Lord, relying on Him, worshiping Him, and everything that is related to that, and that is true and sound, and it is the essence of tawḥeed and devotion.” (Ibn Taymiyyah, Majmoo‘ al-Fatâwâ, 10: 337) This type of fanâ’ is fanâ’ in the Divinity (uloohiyah) of God, and it does not contradict in any way baqâ’, which is subsisting by Allah, with Allah, for Allah.
The second is the perceptual annihilation. Part of this fanâ’ is virtuous and superior. This is where one realizes the existence of the creations, but they never obstruct him or her from beholding the Divine, the Real, the Beginner of all things and the Ultimate Effector and Controller. It is fanâ’ in the Lordship (ruboobiyah) of God when you observe the creations, recognizing their contingency, transience, triviality, and disposability; they will be like glass boards that never block you from seeing through them. When they hurt or benefit you, you see His decrees and His works in their actions. Your response will be cognizant of Him, not them. This is the essence of the station of iḥsân, where you worship Allah as if you see Him. Can you imagine being distracted by anything else (the siwâ) if you are seeing Him?
There is another form of this perceptual fanâ’, which is the dissolution or absorption of the self into the focus of its attention, where the object of absorbed attention acquires an intimacy that belongs to the self, resulting in a state of altered consciousness and causing some people to feel the presence of God to such an extent that they may speak words of disbelief, which are called shaṭaḥât. While such utterances are not commendable and could be considered acts of disbelief if made outside of those states, many scholars, including Imam Ibn Taymiyyah (may Allah bestow mercy on him), maintain that those who make such utterances would be forgiven on account of their spiritual intoxication. (Majmoo‘ al-Fatâwa, 10: 340) He mentioned as an example of those shaṭaḥât the statement of Abu Yazeed al-Bisṭâmi, “Glory be to me.”
For these utterances to be forgiven, however, certain conditions must be fulfilled. The trance should be real, not faked or pretentious, and it should be reached through ḥalâl means. The utterances should be short, only a few words. The person who utters them regrets them upon waking from the trance and even denies them, like Abu Yazeed (may Allah bestow His mercy on him) used to. The person must also be observant of the Sunnah and compliant with the Shari‘ah in his/her religious practice. Finally, as Imam Ibn Taymiyyah clarifies, such utterances were not reported from the best of Allah’s creations: the prophets and the Companions. This is because of the strength of their recognition and intellect and their ability to behold the multiplicity of phenomena and creations while being fully aware of the oneness of the Creator, the Eternal, the Real (glorious is He). Such complete recognition protected them from being overcome by any spiritual trance. Baqâ’ (subsistence) by Allah, with Allah, for Allah is higher than fanâ’ (self-annihilation). It is the essence of Allah’s saying, “until I love him, (so much so that) I become his hearing with which he hears, and his sight with which he sees.” If one sees by Allah and hears by Allah, they will see realities as they truly exist. They will never fall into confusion or illusion (wahm).
The third is the heretical type of fanâ’, which is ontological annihilation (fanâ’ al-wujood) or annihilation of all existences other than the Divine, where it is claimed that nothing exists other than the Lord, inevitably leading to pantheism/monism. This is clearly impossible, but sadly accepted by some. Anyone who claims this type of annihilation should not eat, drink, or breathe if their annihilation into the Divine were real. This would mean that the worshiper is the worshiped and the slave is the Lord. Such heretical views can be dressed in fanciful philosophical or rhetorical arguments to mislead the masses. However, they are diametrically opposed to the Revelation and in fact, they make the Revelation irrelevant. After all, there is no difference between the worship of idols and the worship of God, for the idols, according to these views, are nothing but God. Imam Ibn Ḥajar says:

As for Ahl as-Sunnah, they explained tawḥeed to be the rejection of assimilation and negation (likening God to His creations or stripping Him of His attributes), and this is why al-Junayd said, according to Abu al-Qâsim al-Qushayri’s report, “At-tawḥeed is separating between the Eternal and the originated.” (Fatḥ al-Bâri, 13/344)
⁷⁹² One’s knowledge of Allah being the Creator and the creations being in need of Him for their mere existence makes them aware of their entitlement to nothing other than nothingness, and this is what we were before He brought us into existence. After that, one will be in a state where they lose perception of the siwâ (all else) and deny them. After that, the observer of these facts and states will lose themselves so their annihilation will be fully actualized.
⁷⁹³ Their absorption into the ma‘roof (the Recognized One) makes them lose sense of their own knowledge and knowing.
⁷⁹⁴ He/she denies the siwâ (all else), including his/her own beholding of God.
⁷⁹⁵ There is no doubt that the sheikh did not mean that one’s pursuit of Allah ceases after finding Him in actuality. In fact, the closer one gets to Him, the more ardent is their pursuit of Him and His pleasure. The sheikh meant to say that the person will not feel their pursuit because that feeling will be absorbed into the feeling of their being with Allah. Of the words that capture the stations of fanâ’ and baqâ’ along with the intensity of Allah’s pursuit is this beautiful statement of al-Junayd (may Allah bestow mercy on him) about the love of Allah:

A servant who is detached from himself (ego)

Attached to His Lord through His remembrance

Constantly fulfilling His rights

Beholding Him with his heart

The lights of His majesty/awe burned up his heart

And he subsists only on the nectar of His infinite compassion

The Jabbâr (Irresistible) had manifested to him [his heart] through the veils of the unseen

So, when he speaks, it is by Allah

And whatever utterance he makes, it is from/about Allah

And when he moves, it is by the command of Allah

And when he is still, he is with Allah

So, he is by Allah, for Allah, and with Allah.
⁷⁹⁶ Here, one is trying to lose their beholding of their knowledge, shuhood, and pursuit [of God].
⁷⁹⁷ Here, one is trying to lose their beholding of their fanâ’, because it is only the Real that is to exist. They mean by this the mental, not ontological, reality. After this, one will be qualified to subsist by Allah, with Allah, and for Allah.