Bhagavad Gita Chapter 18.22
yat tu kṛtsna-vad ekasmin
kārye saktam ahaitukam
atattvārtha-vad alpaḿ ca
tat tāmasam udāhṛtam
Translation
And that knowledge by which one is attached to one kind of work as the all in all, without knowledge of the truth, and which is very meager, is said to be in the mode of darkness.