Yājñavalkya Śikṣā 152

152

tvadarthavācinau vovāṃ vā vai yadi nipātajau
ādeśāśca vikalpārthā īṣatspṛṣṭā iti smṛtāḥ

The words vo and vām expressive of the meaning ‘you’, or vā and vai if originating as particles, / and substitutes denoting alternatives, are remembered as slightly touched.