Chapter 18 · Liberation through Renunciation · Krishna said
Bhagavad Gita 18.32 — Tamasic intellect
अधर्मं धर्ममिति या मन्यते तमसावृता। सर्वार्थान्विपरीतांश्च बुद्धिः सा पार्थ तामसी ॥
adharmaṃ dharmamiti yā manyate tamasāvṛtā | sarvārthānviparītāṃśca buddhiḥ sā pārtha tāmasī ||
Meaning
The intellect, covered in darkness, that takes wrong to be right and sees everything upside down is tamasic.