Vaisesika Sūtra 2.1.13

अद्रव्यत्वेन नित्यत्वमुक्तम् ॥१३॥

adravyatvena nityatvamuktam ॥13॥

[adravyatvena = by the non-substance ness; nityatvamuktam = is said to continually existent;]

(As Air) is devoid of substance-ness, it is said to be continually existent.