Bhagwad Gita
Chapter 8, Verse 13
ओमित्येकाक्षरं ब्रह्म व्याहरन्मामनुस्मरन्।
यः प्रयाति त्यजन्देहं स याति परमां गतिम्।।8.13।।
After being situated in this yoga practice and vibrating the sacred syllable om, the supreme combination of letters, if one thinks of the Supreme Personality of Godhead and quits his body, he will certainly reach the spiritual planets.