Vaisesika Sūtra 5.2.19

द्रव्यगुणकर्मनिष्पत्तिवैधर्म्यादभावस्तमः ॥१९॥

The lacuna arising from that which comes forth, contrary to dharma, in substance, quality, and movement is 'tamas', i.e. darkness or ignorance.