Vaisesika Sūtra 3.2.01

आत्मेन्द्रियार्थसंन्निकर्षे ज्ञानस्य भावोऽभावश्च मनसो लिङ्गम् ॥१॥

The presence or lack of knowledge arising from the coming together of ātma, senses, and objects is the indication of mind (manas).