Chapter 18 · verse 39 · gita.yoga.org

Bhagavad Gita 18.39

यदग्रे चानुबन्धे च सुखं मोहनमात्मनः।निद्रालस्यप्रमादोत्थं तत्तामसमुदाहृतम्

That happiness which at first, as well as in the end, deludes the self, and which arises from sleep, indolence, and heedlessness—that is declared to be Tamasic.