The mahāvākyas are four sayings, one traditionally drawn from each of the four Vedas: consciousness is Brahman; I am Brahman; that thou art; this self is Brahman. Advaita treats them as the decisive teaching of scripture, whose meaning, rightly understood, gives liberating knowledge. They were later associated with the four monasteries said to have been founded by Śaṅkara.
Mahāvākya
A “great saying” of the Upaniṣads expressing the unity of the self and Brahman.
Also: Mahavakya, great saying