(The Absolute Truth)
The Truth, The Real, The Embodiment of Truth.
Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is Al-Haqq (in Arabic: ٱلْحَقُّ), meaning: the only reality, the one who is the embodiment of truth, the absolute. Since He is the sole and true God, He has every right to be worshipped. His essence is unavoidable and unchanged.
From the root ha-qaf-qaf (ح ق ق), which has the following classical Arabic connotations: to be suitable, to the requirements of wisdom, justice, truth or fact. To be in accord with the needs of the situation, to be true, right, just, proper. To be genuine, authentic, real, sound, substantial. To be established, confirmed as fact. To be necessary, requisite, justified.
Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ very essence is the truth. There are many layers of His truth. For example, His word is truth (the Qur'an and Messengers), our meeting with Him is truth (resurrection), and His promise is truth (heaven and hell). The truth, by definition, is also never changing. It's absolute or certain. In this manner, only Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is the truth. His existence is enduring and forever. Everything but Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ slowly deteriorates, so how can we trust in anything but Him. The Qur'an mentions, "Indeed, what you are promised is to occur. So when the stars are obliterated And when the heaven is opened And when the mountains are blown away And when the messengers' time has come… For what Day was it postponed? For the Day of Judgement." (Qur'an 77:7-13)
Zaalika bi annal laaha Huwal Haqqu wa anna maa yad'oona min doonihil baatilu wa annal laaha Huwal 'Aliyyul Kabeer (section 3)
"That is because Allah is the Truth, and that what they call upon other than Him is falsehood, and because Allah is the Most High, the Grand." — (Qur'an 31:30)
The understanding that Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is the embodiment of truth is also a testimony to His judgment and knowledge as being perfect. With this understanding, we should adhere to the guidance He set forth. Sometimes, we may find restrictions that seem inconvenient or without cause, but we should realize that we don't always know what's best for us. We must trust Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ knows best. Therefore the believer should show self-restraint and be subservient to the truth.
Fazaalikumul laahu Rabbukumul haqq; famaazaa ba'dal haqqi illad dalaalu fa anna tusrafoon
" For that is Allah, your Lord, the Truth. And what can be beyond truth except error? So how are you averted?" — (Qur'an 10:32)
Summa ruddooo ilallaahi mawlaahumul haqq; alaa lahul hukmu wa Huwa asra'ul haasibeen
"Then are men returned unto Allah, their protector, the (only) reality: Is not His the command? and He is the swiftest in taking account." — (Qur'an 6:62)
Zaalika bi annal laaha Huwal haqqu wa annahoo yuhyil mawtaa wa annahoo 'alaakulli shai'in Qadeer
"That is because Allah is the Truth and because He gives life to the dead and because He is over all things competent" — (Qur'an 22:6)
Zaalika bi annal laaha Huwal haqqu wa anna maa yad'oona min doonihee huwal baatilu wa annal laaha Huwal 'Aliyyul kabeer
"That is because Allah is the Truth, and that which they call upon other than Him is falsehood, and because Allah is the Most High, the Grand." — (Qur'an 22:62)
What is truth?
Many think truth is science, but this is false. There is no objective truth in science. Rather science's whole objective is to disprove that which we currently know. Only in the failure to disprove do we develop some kind of understanding of what is "true," i.e., until it is disproven. This is the scientific process. Its goal is not to provide conclusions but to provide a model of reality consistent with the collective observations of humanity sustained over time.
Things that have been "true" for thousands of years are things that have been thoroughly tested and therefore earned a higher degree of trust. Even then, paradigm shifts exist. There was a time when the predominant view was that the Earth was flat and not round. At one point, diabetes patients were encouraged to eat sugar because it seemed their bodies were just good at removing sugar from their system. So to compensate, doctors suggested eating more sugar to make up for the loss. They only discovered this was not the case through trial and error. It's hard to know the things we don't know. Every generation should have fewer blindspots than the previous, so we can have more confidence now than at any time in the past.
But that's not to say blindspots don't or can't exist. What if the reality we know today is just an illusion? A limitation of our sensory organs or the first layer of a larger painting? We may never know whether our observations are real or just shadows of what is real. The Qur'an states, "The life of this world is nothing but delusion" (Qur'an 57:20). So we've come to the point where we must accept that we know close to nothing. It's freeing... we realize how little anybody knows, and that's a good place to start as it opens the door for humility and exposes us to the openness of all possibilities. The one and only absolue truth we can be sure of is la ilaha illallah muhammadur rasulullah, "There is no deity but Allah. Prophet Muhammad ﷺ is His messenger."
Abu Hanifa and The Atheist:
Ibn Abi al-'Izz reported: It is said that Abu Hanifa, may Allah have mercy on him, was approached by some philosophers who intended to discuss with him the oneness of Allah's Lordship. Abu Hanifa said, "Before we discuss this question, tell me what you think about a boat in the Euphrates, which goes to shore, loads itself with food and other things, then returns, anchors and unloads all by itself, without anyone sailing or controlling it?" They said, "This is impossible." Abu Hanifa said, "If it is impossible with a boat, then how is it possible for the world, in all its vastness, to move by itself?"
The point Abu Hanifa makes is that underlying every assertion - the one who causes it to be is Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ. These things don't need to be exclusive of one another; they can coexist. To be a believer in science is to be a witness and see Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ. You observe and appreciate the manifestation of His creation.
Supplications which include the name Al-Haqq:
It was narrated from Abu Hurairah that the Messenger of Allah (ﷺ) used to say in his Talbiyah: "Labbaika ilahal-haqq, labbaika (Here I am, O god of Truth, here I am)." 
Narrated Ibn Abbas: When the Prophet (ﷺ) got up at night to offer the Tahajjud prayer, he used to say:
اللَّهُمَّ لَكَ الْحَمْدُ أَنْتَ قَيِّمُ السَّمَوَاتِ وَالأَرْضِ وَمَنْ فِيهِنَّ وَلَكَ الْحَمْدُ لَكَ مُلْكُ السَّمَوَاتِ وَالأَرْضِ وَمَنْ فِيهِنَّ وَلَكَ الْحَمْدُ أَنْتَ نُورُ السَّمَوَاتِ وَالأَرْضِ وَلَكَ الْحَمْدُ أَنْتَ الْحَقُّ وَوَعْدُكَ الْحَقُّ وَلِقَاؤُكَ حَقٌّ وَقَوْلُكَ حَقٌّ وَالْجَنَّةُ حَقٌّ وَالنَّارُ حَقٌّ وَالنَّبِيُّونَ حَقٌّ وَمُحَمَّدٌ صلى الله عليه وسلم حَقٌّ وَالسَّاعَةُ حَقٌّ اللَّهُمَّ لَكَ أَسْلَمْتُ وَبِكَ آمَنْتُ وَعَلَيْكَ تَوَكَّلْتُ وَإِلَيْكَ أَنَبْتُ وَبِكَ خَاصَمْتُ وَإِلَيْكَ حَاكَمْتُ فَاغْفِرْ لِي مَا قَدَّمْتُ وَمَا أَخَّرْتُ وَمَا أَسْرَرْتُ وَمَا أَعْلَنْتُ أَنْتَ الْمُقَدِّمُ وَأَنْتَ الْمُؤَخِّرُ لاَ إِلَهَ إِلاَّ أَنْتَ
Allahumma lakal-hamd. Anta qaiyyimus-samawati wal-ard wa man fihinna. Walakal-hamd, Laka mulkus-samawati wal-ard wa man fihinna. Walakal-hamd, anta nurus-samawati wal-ard. Wa lakal-hamd, anta-l-haq wa wa'duka-lhaq, wa liqa'uka Haq, wa qauluka Haq, wal-jannatu Han wan-naru Haq wannabiyuna Haq. Wa Muhammadun, sallal-lahu'alaihi wasallam, Haq, was-sa'atu Haq. Allahumma aslamtu Laka wabika amantu, wa 'Alaika tawakkaltu, wa ilaika anabtu wa bika khasamtu, wa ilaika hakamtu faghfir li ma qaddamtu wama akh-khartu wama as-rartu wama'a lantu, anta-l-muqaddim wa anta-l-mu akh-khir, la ilaha illa anta (or la ilaha ghairuka)
"O Allah! All the praises are for you, You are the Holder of the Heavens and the Earth, And whatever is in them. All the praises are for You; You have the possession of the Heavens and the Earth And whatever is in them. All the praises are for You; You are the Light of the Heavens and the Earth And all the praises are for You; You are the King of the Heavens and the Earth; And all the praises are for You; You are the Truth and Your Promise is the truth, And to meet You is true, Your Word is the truth And Paradise is true And Hell is true And all the Prophets (Peace be upon them) are true; And Muhammad is true, And the Day of Resurrection is true. O Allah! I surrender (my will) to You; I believe in You and depend on You. And repent to You, And with Your help I argue (with my opponents, the non-believers) And I take You as a judge (to judge between us). Please forgive me my previous And future sins; And whatever I concealed or revealed And You are the One who make (some people) forward And (some) backward. There is none to be worshipped but you."
The believer benefits from knowing that Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is Al-Haqq (The Truth). We live following the message of Islam to receive His promise. The Qur'an is the book of truth coming from Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ. It teaches us the basics of enjoying life while honoring our duties. It provides a blueprint for how we should structure our life, what kind of person we should be, the importance of this life, and the greater significance of the next.
 As an aside - This is not meant to be an anti-science remark or stance. I understand it can be controversial, especially with the pandemic and vaccines. The described scientific process is the closest approximation to what is true, but it's far from objective truth. Advocate for skepticism within reason and avoidance of becoming cynical without cause.
 Sahih (Darussalam) Sunan Ibn Majah 2920
 Sahih Al-Bukhari 1120