SSPA. Tat tamasi. You are That. Grand Identity

Tat Tvam Asi (That Thou Art): This is contained in the Chhandogya Upanishad of Sama Veda. This is Upadesha Vakya uttered by the Guru to disciple. Ayam Atma Brahma (This Atman is Brahman): This is contained in the Mandukya Upanishad of the Atharva Veda.