CC Ādi 7.114

tāṅra doṣa nāhi, teṅho ājñā-kārī dāsa
āra yei śune tāra haya sarva-nāśa
Word for word: 
tāṅra — his (Lord Śiva’s); doṣa — fault; nāhi — there is none; teṅho — he; ājñā-kārī — obedient order-carrier; dāsa — servant; āra — others; yei — anyone; śune — hears (the Māyāvāda philosophy); tāra — of him; haya — becomes; sarva-nāśa — everything lost.
Translation: 
“Śaṅkarācārya, who is an incarnation of Lord Śiva, is faultless because he is a servant carrying out the orders of the Lord. But those who follow his Māyāvādī philosophy are doomed. They will lose all their advancement in spiritual knowledge.
Purport: 

Māyāvādī philosophers are very proud of exhibiting their Vedānta knowledge through grammatical jugglery, but in the Bhagavad-gītā Lord Śrī Kṛṣṇa certifies that they are māyayāpahṛta-jñāna, bereft of real knowledge due to māyā. Māyā has two potencies with which to execute her two functions — the prakṣepātmikā-śakti, the power to throw the living entity into the ocean of material existence, and āvaraṇātmikā-śakti, the power to cover the knowledge of the living entity. The function of the the āvaraṇātmikā-śakti is explained in the Bhagavad-gītā by the word māyayāpahṛta-jñānāḥ.

Why the daivī-māyā, or illusory energy of Kṛṣṇa, takes away the knowledge of the Māyāvādī philosophers is also explained in the Bhagavad-gīta by the use of the words āsuraṁ bhāvam āśritāḥ, which refer to a person who does not agree to the existence of the Lord. The Māyāvādīs, who are not in agreement with the existence of the Lord, can be classified in two groups, exemplified by the impersonalist Śaṅkarites of Vārāṇasī and the Buddhists of Saranātha. Both groups are Māyāvādīs, and Kṛṣṇa takes away their knowledge due to their atheistic philosophies. Neither group agrees to accept the existence of a personal God. The Buddhist philosophers clearly deny both the soul and God, and although the Śaṅkarites do not openly deny God, they say that the Absolute is nirākāra, or formless. Thus both the Buddhists and the Śaṅkarites are aviśuddha-buddhayaḥ, or imperfect and unclean in their knowledge and intelligence.

The most prominent Māyāvādī scholar, Sadānanda Yogīndra, has written a book called Vedānta-sāra, in which he expounds the philosophy of Śaṅkarācārya, and all the followers of Śaṅkara’s philosophy attribute great importance to his statements. In this Vedānta-sāra Sadānanda Yogīndra defines Brahman as sac-cid-ānanda combined with knowledge and without duality, and he defines ignorance (jaḍa) as knowledge distinct from that of sat and asat. This is almost inconceivable, but it is a product of the three material qualities. Thus he considers anything other than pure knowledge to be material. The center of ignorance is considered to be sometimes all-pervading and sometimes individual. Thus according to his opinion both the all-pervading Viṣṇu and the individual living entities are products of ignorance.

In simple language, it is the opinion of Sadānanda Yogīndra that since everything is nirākāra (formless), the conception of Viṣṇu and the conception of the individual soul are both products of ignorance. He also explains that the viśuddha-sattva conception of the Vaiṣṇavas is nothing but pradhāna, or the chief principle of creation. He maintains that when all-pervading knowledge is contaminated by the viśuddha-sattva, which consists of a transformation of the quality of goodness, there arises the conception of the Supreme Personality of Godhead, who is the omnipotent, omniscient supreme ruler, the Supersoul, the cause of all causes, the supreme īśvara, etc. According to Sadānanda Yogīndra, because īśvara, the Supreme Lord, is the reservoir of all ignorance, He may be called sarva-jña, or omniscient, but one who denies the existence of the omnipotent Supreme Personality of Godhead is more than īśvara, or the Lord. His conclusion, therefore, is that the Supreme Personality of Godhead (īśvara) is a transformation of material ignorance and that the living entity (jīva) is covered by ignorance. Thus he describes both collective and individual existence in darkness. According to Māyāvādī philosophers, the Vaiṣṇava conception of the Lord as the Supreme Personality of Godhead and of the jīva, or individual soul, as His eternal servant is a manifestation of ignorance. If we accept the judgment of Lord Kṛṣṇa in the Bhagavad- gītā, however, the Māyāvādīs are to be considered māyayāpahṛta-jñāna, or bereft of all knowledge, because they do not recognize the existence of the Supreme Personality of Godhead or they claim that His existence is a product of the material conception (māyā). These are characteristics of asuras, or demons.

Lord Śrī Caitanya Mahāprabhu, in His discourses with Sārvabhauma Bhaṭṭācārya, said:

jīvera nistāra lāgi’ sūtra kaila vyāsa
māyāvādi-bhāṣya śunile haya sarva-nāśa

(Cc. Madhya 6.169)

Vyāsadeva composed the Vedānta-sūtra to deliver the conditioned souls from this material world, but Śaṅkarācārya, by presenting the Vedānta-sūtra in his own way, has clearly done a great disservice to human society, for one who follows his Māyāvāda philosophy is doomed. In the Vedanta-sūtra, devotional service is clearly indicated, but the Māyāvādī philosophers refuse to accept the spiritual body of the Supreme Absolute Person and refuse to accept that the living entity has an individual existence separate from that of the Supreme Lord. Thus they have created atheistic havoc all over the world, for such a conclusion is against the very nature of the transcendental process of pure devotional service. The Māyāvādī philosophers’ unrealizable ambition to become one with the Supreme through denying the existence of the Personality of Godhead results in a most calamitous misrepresentation of spiritual knowledge, and one who follows this philosophy is doomed to remain perpetually in this material world. Therefore the Māyāvādīs are called aviśuddha-buddhayaḥ, or unclean in knowledge. Because they are unclean in knowledge, all their austerities and penances end in frustration. Thus although they may be honored at first as very learned scholars, ultimately they descend to physical activities of politics, social work, etc. Instead of becoming one with the Supreme Lord, they again become one with these material activities. This is explained in Śrīmad-Bhāgavatam (10.2.32):

āruhya kṛcchreṇa paraṁ padaṁ tataḥ
patanty adho ’nādṛta-yuṣmad-aṅghrayaḥ

In actuality the Māyāvādī philosophers very strictly follow the austerities and penances of spiritual life and in this way are elevated to the impersonal Brahman platform, but due to their negligence of the lotus feet of the Lord they again fall down to material existence.