Vaisesika Sūtra 2.2.34

प्रथमाशब्दात् ॥३४॥

prathamāśabdāt ॥34॥

[प्रथम-आ-शब्दात् (prathama-ā-śabdāt) - from the first syllable "ā";]

From the first syllable “ā”.