Bhagavad Gita 6.5 Chapter 6, Verse 5

उद्धरेदात्मनाऽऽत्मानं नात्मानमवसादयेत् ।
आत्मैव ह्यात्मनो बन्धुरात्मैव रिपुरात्मनः ॥६.५॥

uddharedātmanā''tmānaṃ nātmānamavasādayet
ātmaiva hyātmano bandhurātmaiva ripurātmanaḥ

Meaning

Lift yourself up by your own self; do not let yourself sink. For the self alone is one's friend, and the self alone is one's enemy.

Newly written by Bhajan Dhun — scholarly review in progress.

Reference: Bhagavad Gita 6.5 (Chapter 6, The Yoga of Meditation (Atma Samyama Yoga), Verse 5)