Bhagavad Gita 17.11

अफलाकाङ्क्षिभिर्यज्ञो विधिदृष्टो य इज्यते। यष्टव्यमेवेति मनः समाधाय स सात्त्विकः

aphalākāṅkṣhibhir yajño vidhi-driṣhṭo ya ijyate yaṣhṭavyam eveti manaḥ samādhāya sa sāttvikaḥ

That sacrifice which is offered by men without desire for reward, as enjoined by the ordinance (scripture), with a firm faith that doing so is their duty, is Sattvic or pure.

यज्ञ करना कर्तव्य है -- इस तरह मनको समाधान करके फलेच्छारहित मनुष्योंद्वारा जो शास्त्रविधिसे नियत यज्ञ किया जाता है, वह सात्त्विक है।