The Concept Tawhid in Islam
In the name of Allāh, the Most Gracious, the Most Merciful;
All the praise and Thanks is due to Allāh, the Lord of al-‘ālameen. I testify that there is none worthy of worship except Allāh, and that Muhammad, Sallallāhu ‘alayhi wa sallam is His Messenger.
The concept Tawhid in Islam is about Allah’s True Nature and His Oneness, which we acquired it through the Mercy and Guidance of Allah delivered by His prophets and revealed texts,  In order to provide a better understanding of Islamic Tawhid, we have provided a description of Allah and some of His attributes as it appears in a famous, classical text of Islamic knowledge.
The following is an original translation of excerpts from Revival of the Religious Sciences by Imam Abu Hamid Al-Ghazali :
Allah is singular in His essence with no partner, Unique with no equivalent, Absolute, no opposite has He, Alone without peer. He is beginning less without predecessor, perpetual of being without end, singularly sustaining everything without stop. He is not victim to termination or cessation, or to the elapsing of spans or the passing of interims. Rather He is the First and the Last; the Outward and the Inward – and He has knowledge of everything.
He is not a body with form, nor is He a confined or quantifiable substance. He does not resemble bodies in quantifiably or divisibility. Rather He resembles nothing existent, nor does anything existent resemble Him. There is absolutely nothing like Him, nor is He like anything.
No measure confines Him, no space contains Him, no direction encompasses Him, nor do the heavens surround Him.
He is above everything until the farthest reaches of the stars – an above-ness that does not increase His nearness to the heavens; rather He is exalted in degree above the heavens to the same extent that He is exalted in degree above the depths of the earth. Notwithstanding, He is near to all existence, and He is nearer to the bondsman than his jugular vein. His nearness, however, no more resembles the nearness of bodies one to another than His essence resembles the essences of bodies.
He is too sublime that space should encompass Him, as He is too hallowed that time should restrict Him. Rather He was, before He created time and space, and He is now as He was always. He is separate from His creation by His attributes. He is transcendentally holier than to be subject to change and movement. Rather He remains in His qualities of absolute majesty, not subject to abating, and in His qualities of perfection with no need of increase.
He is Living, Almighty, Irresistible, Overpowering; deficiency does not affect Him nor does incapacity. “No slumber can seize Him nor sleep.”  Extinction and death do not counteract Him. He is possessed of absolute dominion, sovereignty, and grandeur; to Him is creation and command.
He is matchless in creating and beginning, solitary in causing existence and originating. He creates all beings and their acts, decrees their sustenance and spans. Nothing possible is outside His grasp, and He is never detached from the absolute governing of all affairs. His abilities cannot be enumerated, and His knowledge is boundless.
He knows all things knowable, encompassing all that transpires between the depths of the earths to the ends of the universe. Nothing of an atom’s weight in the earth and the heavens escapes His Knowledge; rather He knows the creeping of a black ant across a soundless stone on a lightless night. He knows the movement of the particles on a windy day. He knows the hidden and what is beyond. He presides over the thoughts of the conscience, the movements of the cerebrations, and the recondite subtleties of the psyche, with a beginningless, eternal Knowledge that has been with Him forever.
He is the willer of all that exists, and He is the director of all that occurs. Nothing occurs in the seen or unseen world, be it minimal or abundant, small or large, good or evil, beneficial or harmful, of belief or disbelief, knowledge or ignorance, triumph or ruin, increase or decrease, obedience or defiance, except by His decree, foreordainment, command, and volition. What He wills is, and what He does not will is not.
A servant has no escape from disobeying Him except through His conferred success and mercy; he has no power to obey Him except through His assistance and will. If all of mankind united together to move or retard a single atom in the universe without His will and volition, they would be unable to do so.
He hears and He sees. No audible thing, however faint, escapes His hearing, and no visible thing, however minute, is hidden from His sight. Distance does not impede His hearing and darkness does not obstruct His seeing. His attributes do not resemble the attributes of the creation to the same extent that His essence does not resemble the essences of creation.
Everything other than Him is an originated thing that He created by His power from nothingness, since He existed in eternity alone and there was nothing whatsoever with Him. He originated creation thereafter as a manifestation of His power and as a realization of His preceding Will, not because He had any need of it.
He is Magnanimous in creating and in imposing obligations upon His creation; He is not compelled to do it by necessity. He is Gracious in beneficence and reform, though not through any need. Munificence and Kindness, Beneficence and Grace are His. He rewards His believing worshipers for their acts of obedience according to generosity and encouragement rather than according to their merit and obligation, for there is no obligation upon Him in any deed towards anyone. Tyranny is inconceivable in Him, for there is no right upon Him towards anyone. 
While these are the Islamic beliefs on Allah in written form, it must be noted that a person is not accountable for his intellectual understanding of them, but rather he is responsible for truly incorporating them in his heart. True conviction in Allah’s existence and in His actual relationship with every one of us comes only with His Mercy and Guidance. As such, Muslims ask Allah in every prayer (solah and do’a) for guidance unto His Straight Path.
And Allāh Almighty Knows best.
 For a more-detailed presentation of these concepts, see Introducing Islam’s “Messengers” and “Revelation” sections respectively.
 A famous Islamic jurist, theologian, and sage who died in the beginning of the 6th century after Hijrah (1111 CE).
 Surah Al-Baqarah, 2: 255.
 This passage was an original translation of excerpts of al-Ghazali’s “Foundations of Belief,” found in Book II of his Revival of the Religious Sciences. A fuller version of the section can be found on the Dartmouth College MSA website.
[Excerpted from IslamOnline]