Bhagavad Gita 18.23
An obligatory action done by one who is disinterested, who neither likes nor dislikes it, and gives no thought to the consequences that may follow, such an action is Pure.
नियतं सङ्गरहितमरागद्वेषतः कृतम्।अफलप्रेप्सुना कर्म यत्तत्सात्त्विकमुच्यते॥niyataṃ saṅgarahitamarāgadveṣataḥ kṛtam|aphalaprepsunā karma yattatsāttvikamucyate||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).