Chapter 2 · The Yoga of Knowledge · Krishna said
Bhagavad Gita 2.57 — Neither elated nor bitter
यः सर्वत्रानभिस्नेहस्तत्तत्प्राप्य शुभाशुभम्। नाभिनन्दति न द्वेष्टि तस्य प्रज्ञा प्रतिष्ठिता ॥
yaḥ sarvatrānabhisnehastattatprāpya śubhāśubham | nābhinandati na dveṣṭi tasya prajñā pratiṣṭhitā ||
Meaning
One who is unattached everywhere, who neither rejoices on getting good nor hates on getting bad — that person's wisdom is steady.