Bhagavad Gita 16.24
Therefore, whenever there is doubt as to whether you should do something or not, let the scriptures guide your conduct. In the light of the scriptures, you should labor your whole life.
तस्माच्छास्त्रं प्रमाणं ते कार्याकार्यव्यवस्थितौ।ज्ञात्वा शास्त्रविधानोक्तं कर्म कर्तुमिहार्हसि॥tasmācchāstraṃ pramāṇaṃ te kāryākāryavyavasthitau|jñātvā śāstravidhānoktaṃ karma kartumihārhasi||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).