Bhagavad Gita 14.8तमस्त्वज्ञानजं विद्धि मोहनं सर्वदेहिनाम्।प्रमादालस्यनिद्राभिस्तन्निबध्नाति भारत ॥

Tamas is that binding force with a tendency to lethargy, sloth and foolish actions. It causes delusion or nondiscrimination. It binds him who associates the Self with the body. A Tamasic man acts under the compulsion of the wants of the body. He has no power of judgment. Troubled by the wants of the body he acts under pressure to keep himself alive. His actions are not guided by reason. They are on the plane of instinct. His senses are dull. He becomes infatuated and stupefied. He has no inclination to work. He yawns much. He sleeps too much. He always wants to sleep. He nevr knows when and how to act, what, to whom and how to talk. He takes delight in following the wrong path. He does not know how to behave or how to address others. He is thoughtless and ignorant. He forgets everything. He is negligent and indolent. He is just in a stage higher than lifeless matter.He who is under the grip of heedlessness (Pramada) is not able to discriminate between the eternal and the noneternal. This is an enemy of illumination, the effect of Sattva. He who is overpowered by laziness (Alasya) is not able to exert. This is an enemy of Pravritti, the effect of Rajas. Sleep (Nidra) is LayaVritti, (a state of absorption into ignorance) which is dependent on Tamas. This is the enemy of the works done by Sattva and Rajas.