Bhagavad Gita 6.32
आत्मौपम्येन सर्वत्र समं पश्यति योऽर्जुन। सुखं वा यदि वा दुःखं स योगी परमो मतः।।6.32।।
ātmaupamyena sarvatra samaṃ paśyati yo'rjuna| sukhaṃ vā yadi vā duḥkhaṃ sa yogī paramo mataḥ||6.32||
atmaupamyena sarvatra samam pashyati yo'rjuna sukham va yadi va duhkham sa yogi paramo matah6.32
Meaning
Arjuna, that yogi is considered the highest who judges the pleasure and pain of all beings by the same standard as they would apply to themselves — the golden rule of spiritual life.
हे अर्जुन! जो पुरुष अपने समान सर्वत्र सम देखता है, चाहे वह सुख हो या दुःख, वह परम योगी माना गया है।
This is verse 32 of 47 in Chapter 6 (Dhyana Yoga) of the Bhagavad Gita.