Bhagavad Gita Chapter 18, Verse 26

मुक्तसङ्गोऽनहंवादी धृत्युत्साहसमन्वितः | सिद्ध्यसिद्ध्योर्निर्विकारः कर्ता सात्त्विक उच्यते ||

mukta-saṅgo 'nahaṁvādī dhṛty-utsāha-samanvitaḥ siddhy-asiddhyor nirvikāraḥ kartā sāttvika ucyate

The doer who is free from attachment, without ego-speech, endowed with firmness and enthusiasm, and unaffected by success or failure, is called sattvic.

Krishna begins explaining the three kinds of doer, starting with the sattvic doer. 'Mukta-saṅgo 'nahaṁvādī'—free from attachment (mukta-saṅgaḥ), without ego-speech (anahaṁvādī), meaning not claiming 'I am the doer'. 'Dhṛty-utsāha-samanvitaḥ'—endowed with (samanvitaḥ) firmness (dhṛti) and enthusiasm (utsāha). 'Siddhy-asiddhyor nirvikāraḥ'—unaffected (nirvikāraḥ) by success (siddhi) or failure (asiddhyoḥ). 'Kartā sāttvika ucyate'—the doer (kartā) is called (ucyate) sattvic (sāttvikaḥ). This is the sattvic doer: free from attachment, not claiming 'I am the doer', steady and enthusiastic, unaffected by success or failure. This is the highest kind of doer: detached, humble, balanced. You perform action without attachment, without ego, with steadiness and enthusiasm, unaffected by outcomes. This is the path: acting as a doer without attachment to the sense of doing, without ego, with balance.