tasmāc chāstraṁ pramāṇaṁ
tasmāc chāstraṁ pramāṇaṁ te kāryākārya-vyavasthitau |
jñātvā śāstra-vidhānoktaṁ karma kartum ihārhasi ||
(Śrīmad Bhagavad-gītā: 16.24)
“Therefore, śāstra is the pramāṇa [i.e., means of knowledge] in determining what is to be done and not to be done. By understanding the stated injunctions of the śāstra hereto [i.e., in regard to karma], you become fit to perform it.”