Bhagavad Gītā Chapter Five verse 17

tadbuddhayas tadātmānas tanniṣṭhās tatparāyaṇāḥ |
gacchantyapunarāvṛttiṃ jñānanirdhūtakalmaṣāḥ ||

tat - that, thisbuddhi - the intellectual faculty; comprehension; intelligence, discernment, judgementātman - essence; the highest personal principle of lifeniṣṭhā - firmness, steadiness, skill in, familiarity with, certain knowledge ofjñāna - knowing; knowledge; higher knowledge

Commentaries and Reflections

TKV Desikachar:

Niṣṭhā
The holding of a question throughout the days activities.