Śaiśirīya Śikṣā 8

8

duspṛṣṭaśceti vijñeyo nāsikyaṃ raṅgamucyate
uccāraṇaviśeṣeṇātrākṣarāśrayamucyate

and the duspṛṣṭa is to be recognized, [and] the nasal is called raṅga. / According to distinct pronunciation here, it is said to depend on syllables.