Bhagavad Gita 6.23
This inner severance from the affliction of misery is spirituality. It should be practiced with determination and with a heart that refuses to be depressed.
तं विद्याद् दुःखसंयोगवियोगं योगसंज्ञितम्।
स निश्चयेन योक्तव्यो योगोऽनिर्विण्णचेतसा॥taṃ vidyād duḥkhasaṃyogaviyogaṃ yogasaṃjñitam|
sa niścayena yoktavyo yogo'nirviṇṇacetasā||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).