Vaisesika Sūtra 3.1.17

यस्माद् विषाणी तस्मादश्वः ॥१७॥

yasmād viṣāṇī tasmād aśvaḥ ॥17॥

[यस्मात् (yasmāt) - because of which; विषाणी (viṣāṇī) - having horns; तस्मात् (tasmāt) - therefore; अश्वः (aśvaḥ) - it is a horse.]

Because it has horns, therefore it is a horse.
(Note: This sūtra is intentionally ironic or illustrative of faulty reasoning.)