Bhagwad Gita
Chapter 2, Verse 15
यं हि न व्यथयन्त्येते पुरुषं पुरुषर्षभ।
समदुःखसुखं धीरं सोऽमृतत्वाय कल्पते।।2.15।।
O best among men [Arjuna], the person who is not disturbed by happiness and distress and is steady in both is certainly eligible for liberation.