Śatapatha Brāhmaṇa ("of a hundred paths") 5.4.1.16

5.4.1.16

naitenodgṛhṇīyāt | mitro 'si varuṇo 'sītyevodgṛhṇīyādbāhū vai mitrāvaruṇau bāhubhyāṃ vai rājanyo maitrāvaruṇastasmānmitro 'si varuṇo 'sītyevodgṛhṇīyāt

Let him not lift up (the king's arms) with that one, but let him rather lift them up with, 'Thou art Mitra, thou art Varuna;' for Mitra-Varuna are the two arms, and by his arms the Râganya belongs to Mitra and Varuna: let him therefore lift up his arms with, 'Thou art Mitra, thou art Varuna.'