Shatapatha Brahmana 6.3.1.34

6.3.1.34

anyataḥkṣṇutsyāt | anyatararo hīdaṃ vācaḥ kṣṇutamubhayataḥkṣṇuttveva bhavatyubhayato hīdaṃ vācaḥ kṣṇutaṃ yadenayā daivaṃ ca vadati mānuṣaṃ cātho yatsatyaṃ cānṛtaṃ ca tasmādubhayataḥkṣṇut

It may be sharp on one side only, for on one of the two sides is there a keen edge to this speech of ours. But indeed it is one that is sharp on both sides, for on both sides is there a keen edge to this speech of curs, inasmuch as it speaks both what is divine and what is human, and both truth and untruth: therefore it is one that is sharp on both sides.