Bhagavad Gita 8.13

Repeating Om, the symbol of eternity, and holding Me always in remembrance, he who thus leaves his body and goes forth reaches the Supreme Spirit.

ओमित्येकाक्षरं ब्रह्म व्याहरन्मामनुस्मरन्।
यः प्रयाति त्यजन्देहं स याति परमां गतिम्॥

omityekākṣaraṃ brahma vyāharanmāmanusmaran|
yaḥ prayāti tyajandehaṃ sa yāti paramāṃ gatim||

English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).