Question: I have seen the following argument in several places:

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> Consciousness cannot be an illusion, and it surely exists.
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> An illusion is perceiving something to be true when this something is not actually the case. "Perceiving" and "being conscious of" can be taken to be synonymous, so saying that consciousness is an illusion is a contradiction.
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The argument is very strong as it relies on semantics.

**What is the first written philosophical account of this argument?**

Answer: 
Upanishads would be the earliest. One of the *Mahavakyas* ('Great Sayings') of the Upanishads (there are 4 in total) is *Prajnanam Brahma* - Consciousness is Brahman. It appears in the *Aitareya Upanishad* III. i. 3. The *Aitareya Upanishad* is part of the *Rig Veda*, considered by many as the oldest Veda. Most consider the Vedas at least 1500 BC. Verses 2-3 says (Swami Nikhilananda translator):

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> It is the heart and mind. It is [known in accordance with its different functions, as] consciousness, lordship, knowledge [of arts], wisdom, retentive power of mind, sense knowledge, steadfastness, thought, thoughtfulness, sorrow, memory, concepts, purpose, life, desire, longing [for sense-objects]: all these are but various names of Consciousness (Prajnanam).
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> He is Brahman, He is Indra, He is Prajapati: He is all these gods; He is the five great elements--earth, air, akasa [space], water, light; He is all these small creatures and the others which are mixed [with them]; He is the origin [of the moving and unmoving]--those born of an egg, of a womb, of sweat, and of a sprout; He is horses, cows, human beings, elephants--whatever breathes here, whether moving on legs or flying in the air or unmoving. All this is guided by Consciousness (Prajnanam), is supported by Consciousness. The basis [of the universe] is Consciousness. Consciousness is Brahman. 
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Upanishads are earlier recorded arguments on consciousness and other internal phenomena.
You can browse various translations of these scriptures in English.

P.S. It seems any reference to Indian Philosophies are getting negative voting on this site. 

Edit: Aitareya Upanisad from the rigveda which is older than any given scripture.

An English translation of one of the Sloka:

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> III-i-3: This One is (the inferior) Brahman; this is Indra, this is Prajapati; this is all these gods; and this is these five elements, viz. earth, air, space, water, fire; and this is all these (big creatures), together with the small ones, that are the procreators of others and referable in pairs – to wit, those that are born of eggs, of wombs, of moisture of the earth, viz. horses, cattle, men, elephants, and all the creatures that there are which move or fly and those which do not move. **All these have Consciousness as the giver of their reality; all these are impelled by Consciousness; the universe has Consciousness as its eye and Consciousness is its end. Consciousness is Brahman.** 
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Here you guys can find numerous iterations of consciousness word.

Other Upanishad from Rigveda:

Aitareya 

Atmabodha 

Kaushitaki 

Mudgala 

Nirvana 

Nadabindu 

Akshamaya 

Tripura 

Bahvruka

Saubhagyalakshmi