Skanda Purana 1.4.3.38

1.4.3.38

munīnāṃ yatra paramaṃ sthānaṃ cāpyavināśakṛt..
svāhāsvadhāvaṣaṭkāra hantakāro na naśyati.. 5.38 ..

where there is the supreme and imperishable abode of the sages, / and the utterances svāhā, svadhā, vaṣaṭ, and hanta never perish;