Bg 18.30

pravṛttiṁ ca nivṛttiṁ ca
kāryākārye bhayābhaye
bandhaṁ mokṣaṁ ca yā vetti
buddhiḥ sā pārtha sāttvikī
Synonyms: 
pravṛttim — doing; ca — also; nivṛttim — not doing; ca — and; kārya — what ought to be done; akārye — and what ought not to be done; bhaya — fear; abhaye — and fearlessness; bandham — bondage; mokṣam — liberation; ca — and; — that which; vetti — knows; buddhiḥ — understanding; — that; pārtha — O son of Pṛthā; sāttvikī — in the mode of goodness.
Translation: 
O son of Pṛthā, that understanding by which one knows what ought to be done and what ought not to be done, what is to be feared and what is not to be feared, what is binding and what is liberating, is in the mode of goodness.
Purport: 

Performing actions in terms of the directions of the scriptures is called pravṛtti, or executing actions that deserve to be performed. And actions which are not so directed are not to be performed. One who does not know the scriptural directions becomes entangled in the actions and reactions of work. Understanding which discriminates by intelligence is situated in the mode of goodness.