Bhagavad Gita · 18.22

यत्तु कृत्स्नवदेकस्मिन्कार्ये सक्तमहैतुकम्।अतत्त्वार्थवदल्पं च तत्तामसमुदाहृतम्॥

yat tu kṛitsnavad ekasmin kārye saktam ahaitukam atattvārthavad alpaṁ cha tat tāmasam udāhṛitam

But that knowledge which clings to one single effect as if it were the whole, without reason, without basis in truth, and trivial — that is declared to be tamasic.

— Bhagavad Gita 18.22

Source: Sacred-Texts.com (Sanskrit) + Bhagavad-Gita.io (translations)