अफलाकाङ्क्षिभिर्यज्ञो विधिदृष्टो य इज्यते।यष्टव्यमेवेति मनः समाधाय स सात्त्विकः
aphalākāṅkṣhibhir yajño vidhi-driṣhṭo ya ijyate yaṣhṭavyam eveti manaḥ samādhāya sa sāttvikaḥ
Sacrifice is pure when it is offered by one who does not covet the fruit of it, when it is done according to the commands of scripture, and with implicit faith that the sacrifice is a duty.
Translated by Shri Purohit Swami
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.
Translated by Swami Sivananda
Word meanings (from the gita/gita dataset)
aphala-ākāṅkṣhibhiḥ—without expectation of any reward; yajñaḥ—sacrifice; vidhi-driṣhṭaḥ—that is in accordance with the scriptural injunctions; yaḥ—which; ijyate—is performed; yaṣhṭavyam-eva-iti—ought to be offered; manaḥ—mind; samādhāya—with conviction; saḥ—that; sāttvikaḥ—of the nature of goodness