Bhagavad Gita Chapter 18, Verse 9

कार्यमित्येव यत्कर्म नियतं क्रियतेऽर्जुन | सङ्गं त्यक्त्वा फलं चैव स त्यागः सात्त्विको मतः ||

kāryam ity eva yat karma niyataṁ kriyate 'rjuna saṅgaṁ tyaktvā phalaṁ caiva sa tyāgaḥ sāttviko mataḥ

O Arjuna, that action which is performed as duty, having abandoned attachment and fruit, is considered sattvic relinquishment.

Krishna explains the third and proper kind of relinquishment: sattvic tyaga. 'Kāryam ity eva yat karma niyataṁ kriyate'—that action (karma) which is performed (kriyate) as duty (kāryam), as prescribed (niyatam). 'Saṅgaṁ tyaktvā phalaṁ caiva'—having abandoned attachment (saṅgam tyaktvā) and fruit (phalam). 'Sa tyāgaḥ sāttviko mataḥ'—that relinquishment (tyāgaḥ) is considered (mataḥ) sattvic (sāttvikaḥ). This is the proper kind of tyaga: performing prescribed duty (not abandoning it) while relinquishing attachment to both the action and its fruits. This is sattvic because it comes from understanding, not from delusion (tamasic) or fear (rajasic). You perform duty because it's duty, not because you're attached to it or its results. This is the path: duty without attachment to action or fruits.