Kautilya's Arthashastra 3.11.35

3.11.35

tatra brāhmaṇaṃ brūyāt "satyaṃ brūhi" iti //

Witness shall be taken before Bráhmans, vessels of water and fire. A Bráhman witness shall be told ‘Tell the truth’; a Kshatriya or a Vaisya witness shall be told thus:--‘If thou utterest falsehood, thou, do not attain the fruit of thy sacrificial and charitable deeds; but having broken the array of thy enemies in war, thou, do go a beggar with a skull in thy hand.’