We know that Nirguna Brahman is Sat, Chit and Ananda.
Are not Sat, Chit and Anandas themselves gunas? As they are qualities.
Reference, Tattva Bodha of Shri Shankaracharya.
Any characteristic is pointed out by three methods
(a) By distinguishing it from others – Vyavartaka Lakshana – the house is the second building from the petrol pump.
(b) By pointing out its apparent attributes – Tatastha Lakshana – the house where the dog is sitting at the door.
(c) By describing its essential nature – Svrupa Lakshana – the house is made of bricks
Thus, for the above it can be said, the vyavartaka lakshana of Atman is that it is different from non-self of Buddhism. It has apparent attributes wherein it is the substratum of the world and its essential nature of Sat-Chit-Ananda.
“Brahman is Existence, Consciousness, Infinitude.” —Taitt. Up., II. 1.
“Brahman is Consciousness, Bliss.” —Brih. Up., III. 9. 28.
Technically, Brahman is indescribable, as said in Mandukya Karika verse 7.
नान्तःप्रज्ञं न बहिःप्रज्ञं नोभयतःप्रज्ञं न प्रज्ञानघनं न प्रज्ञं नाप्रज्ञम् | अदृश्यमव्यवहार्यमग्राह्यमलक्षणमचिन्त्यमव्यपदेश्यमेकात्मप्रत्ययसारं प्रपञ्चोपशमं शान्तं शिवमद्वैतं चतुर्थं मन्यन्ते स आत्मा स विज्ञेयः || 7 ||
nāntaḥprajñaṃ na bahiḥprajñaṃ nobhayataḥprajñaṃ na prajñānaghanaṃ na prajñaṃ nāprajñam | adṛśyamavyavahāryamagrāhyamalakṣaṇamacintyamavyapadeśyamekātmapratyayasāraṃ prapañcopaśamaṃ śāntaṃ śivamadvaitaṃ caturthaṃ manyante sa ātmā sa vijñeyaḥ || 7 ||
Turīya is not that which is conscious of the internal (subjective) world, nor that which is conscious of the external (objective) world, nor that which is conscious of both, nor that which is a mass all sentiency, nor that which is simple consciousness, nor that which is insentient. (It is) unseen (by any sense organ), not related to anything, incomprehensible (by the mind), uninferable, unthinkable, indescribable, essentially of the nature of Consciousness constituting the Self alone, negation of all phenomena, the Peaceful, all Bliss and the Non-dual. This is what is known as the fourth (Turīya). This is the Ātman and it has to be realised.
These should not be taken as gunas. The qualities which give svarupa lakshana are identical with the thing itself and last as long as the thing last. Fire is hot. You can not get fire which is cold. Thus the svarupa lakshana of Brahman should consist of only lakshanas that are eternal. Otherwise, Brahman will not be eternal.
Brahman is that which is permanent in things that change. Existence can never change, never perish, though things perish. Existence is the nature of Reality and is different from the things of form and name. Clay is always existent while pots and pans may perish and become clay again.
What is the nature of this Absolute Existence? We cannot make a distinction between our existence and our consciousness. Just as we cannot deny existence, so also we cannot deny consciousness. We can deny the states of consciousness, but we can never deny consciousness itself. Universal Consciousness is not to be confused with the individual’s ego-consciousness. It is Pure Awareness. Consciousness in the sense of Reality does not imply that outside it something must exist as its object. In the highest condition, the existence and the content of consciousness are one and the same. Thus it is completely non-dual. There is only subject and no object.
Then, in this state where is only subject and no object, is it a blankness or shunya? Is it devoid of anything? The upanishads clarify
"Where there is neither seeing nor hearing nor knowing of anything else which is a second entity—that is the Infinite” (Chh. Up., VII. 23, 24).
“This Being (of Brahman) is the supreme Bliss.” —Brih Up., IV. 3. 32.
Absolute Existence which is Absolute Knowledge is also Absolute Bliss. Self is of the nature of absolute Bliss as it is free from all wants, because it is absolute and includes everything in itself.
In this context, the following bhAshya of Adi Sankaracharya on Brihadaranyaka upanishad 2.3.6 is relevant.
अध्यारोपितनामरूपकर्मद्वारेण ब्रह्म निर्दिश्यते ‘विज्ञानमानन्दं ब्रह्म’ (बृ. उ. ३ । ९ । २८) ‘विज्ञानघन एव ब्रह्मात्मा’ (बृ. उ. २ । ४ । १२) इत्येवमादिशब्दैः । यदा पुनः स्वरूपमेव निर्दिदिक्षितं भवति निरस्तसर्वोपाधिविशेषम् , तदा न शक्यते केनचिदपि प्रकारेण निर्देष्टुम् ; तदा अयमेवाभ्युपायः — यदुत प्राप्तनिर्देशप्रतिषेधद्वारेण ‘नेति नेति’ (बृ. उ. २ । ३ । ६) इति निर्देशः ॥
Brahman is described by means of name, form and action superimposed on It, in such terms as, ‘Knowledge, Bliss, Brahman’ (III. ix. 28), and ‘Pure Intelligence’ (II. iv. 12), ‘Brahman,’ and ‘Atman.’ When, however, we wish to describe Its true nature, free from all differences due to limiting adjuncts, then it is an utter impossibility. Then there is only one way left, viz. to describe It as ‘Not this, not this,’ by eliminating all possible specifications of It that one may know
So strictly speaking, it is not nirguNa brahman that is directly being described by the terms sat, chit and Ananda.
That describing brahman directly is impossible is also stated by Sri Sankaracharya in Brahma sutra bhashya
Of a similar purport is that scriptural passage which relates how Bâhva, being questioned about Brahman by Vashkalin, explained it to him by silence, 'He said to him, "Learn Brahman, O friend," and became silent. Then, on a second and third question, he replied, "I am teaching you indeed, but you do not understand. Silent is that Self."' The same teaching is conveyed by those Smriti-texts which deny of Brahman all other characteristics; so, e.g. 'I will proclaim that which is the object of knowledge, knowing which one reaches immortality; the highest Brahman without either beginning or end, which cannot be said either to be or not to be' (Bha. Gîtâ XIII, 13).
Below is the quotation from Gita referred above -
ज्ञेयं यत्तत्प्रवक्ष्यामि यज्ज्ञात्वाऽमृतमश्नुते। अनादिमत्परं ब्रह्म न सत्तन्नासदुच्यते।।13.13।।
In the above quotation from Gita, brahman is considered as neither sat nor asat.