Bhagavad Gita 2.48:

yogasthah kuru karmani sangam tyaktva dhananjaya siddhyasiddhyoh samo bhutva samatvam yoga uchyate

"Live then in yoga, O King of Riches, and give up all attachment to actions. We call it "yoga" when you reach that balance where success and failure are all the same."

translation by Geshe Michael Roach and Lama Christie McNally