Mandukya Karika, verse 3.17


स्वसिद्धान्तव्यवस्थासु द्वैतिनो निश्चिता दृढम् ।
परस्परं विरुध्यन्ते तैरयं न विरुध्यते ॥ १७ ॥

svasiddhāntavyavasthāsu dvaitino niścitā dṛḍham |
parasparaṃ virudhyante tairayaṃ na virudhyate || 17 ||

17. The dualists obstinately cling to the conclusions arrived at by their own enquiries (as being the truth). So they contradict one another; whereas the Advaitin finds no conflict with them.

Shankara Bhashya (commentary)

The knowledge of the non-dual Self is established by both Scriptures and reasoning. Therefore, it is alone the perfect knowledge. Other views, on account of their being devoid of the bases of Scriptures and reasoning, lead to false systems. The views of the dualists are false on account of this additional reason, that they are the fruitful sources of the vices of attachment and hatred, etc. How is this? The dualists following the views of Kapila, Kanāda, Buddha and Jina, etc., hold firmly to the conclusions as outlined and formulated by their respective schools. They1 think that the view they hold is alone the ultimate Reality, whereas other views are not so. Therefore they become attached to their own views and hate others whom they consider to be opposed to them. Thus being overcome with attachment and hatred, they contradict one another, the reason being the adherence to their own convictions as the only truth. But our view, viz., the unity of Ātman, based upon the identity of all, supported by the Vedas, does not conflict with others who find contradictions among themselves,—as2 one’s limbs such as hands, feet, etc., do not conflict with one another. Hence the purport of the Śruti is that the knowledge of the oneness of Ātman, as it is free from the blemish of attachment and aversion, is the true knowledge. This Karikā proves the superiority of the Advaita knowledge over other views as it does not contradict the Scriptural statements regarding creation and exercises (Upāsana), and also because it does not clash with other theories. Advaita alone harmonises all other doctrines and theories. It alone gives the rationale of other relative views regarding Truth.