Bg 8.13

om ity ekaksaram brahma
vyaharan mam anusmaran
yah prayati tyajan deham
sa yati paramam gatim

Word for word: 
om — the combination of letters om (om-kara); iti — thus; eka-aksaram — the one syllable; brahma — absolute; vyaharan — vibrating; mam — Me (Krishna); anusmaran — remembering; yah — anyone who; prayati — leaves; tyajan — quitting; deham — this body; sah — he; yati — achieves; paramam — the supreme; gatim — destination.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
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.

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
It is clearly stated here that om, Brahman and Lord Krishna are not different. The impersonal sound of Krishna is om, but the sound Hare Krishna contains om. The chanting of the Hare Krishna mantra is clearly recommended for this age. So if one quits his body at the end of life chanting Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare, he certainly reaches one of the spiritual planets, according to the mode of his practice. The devotees of Krishna enter the Krishna planet, Goloka Vrndavana. For the personalists there are also innumerable other planets, known as Vaikuntha planets, in the spiritual sky, whereas the impersonalists remain in the brahma-jyotir.