OM

 Indian: “Meditate on Brahman with the help of the syllable OM. Cross the fearful currents of the ocean of worldliness by means of the raft of Brahman-the sacred syllable OM” (Svet. Up.* 2:8). “Uttering the sacred syllable OM and meditating upon me. Such a man reaches the highest goal” (BG* 8:13; cf. Tait. Up. 1:8)