From wiki:
The Mahavakyas (sing.: mahāvākyam, महावाक्यम्; plural: mahāvākyāni, महावाक्यानि) are "The Great Sayings" of the Upanishads, as characterized by the Advaita school of Vedanta.
Most commonly, Mahavakyas are considered four in number -
- Prajnanam Brahma (प्रज्ञानम् ब्रह्म)
- Aham Brahma Asmi (अहम् ब्रह्म अस्मि)
- Tat Tvam Asi (तत् त्वम् असि)
- Ayam Atma Brahma (अयम् आत्मा ब्रह्म)