Bhagavad Gita
Chapter 2 · Verse 14
मात्रास्पर्शास्तु कौन्तेय शीतोष्णसुखदुःखदाः। आगमापायिनोऽनित्यास्तांस्तितिक्षस्व भारत॥
mātrā-sparśās tu kaunteya śītoṣṇa-sukha-duḥkha-dāḥ, āgamāpāyino 'nityās tāṁs titikṣasva bhārata
Sensation and circumstance are always in motion. Neither discomfort nor pleasure is permanent, and steadiness comes from not over-identifying with either while it passes through.
This too shall pass. Meet both joy and sorrow with the same steady heart.