Bhagavad Gītā Chapter Five verse 17

tadbuddhayas tadātmānas tanniṣṭhās tatparāyaṇāḥ |
gacchantyapunarāvṛttiṃ jñānanirdhūtakalmaṣāḥ ||

ātman - essence; the highest personal principle of lifejñāna - knowing; knowledge; higher knowledgebuddhi - comprehensionniṣṭhā - persistance

Commentaries and Reflections

TKV Desikachar:

Niṣṭhā
The holding of a question throughout the days activities.