Bhagwad Gita
Chapter 6, Verse 5
उद्धरेदात्मनाऽऽत्मानं नात्मानमवसादयेत्।
आत्मैव ह्यात्मनो बन्धुरात्मैव रिपुरात्मनः।।6.5।।
A man must elevate himself by his own mind, not degrade himself. The mind is the friend of the conditioned soul, and his enemy as well.