Śatapatha Brāhmaṇa ("of a hundred paths") 6.4.4.10

6.4.4.10

athājasya | ṛtaṃ satyamṛtaṃ satyamityayaṃ vā agnirṛtamasāvādityaḥ satyaṃ yadi vāsāvṛtamayaṃ satyamubhayamvetadayamagnistasmādāha 'rtaṃ satyamṛtaṃ satyamiti tadenamajena sambharati

Then (he holds it over) the he-goat, with (Vâg. S XI, 47), 'The law--the truth, the law--the truth!'--the (divine) law doubtless is this Agni; and the truth is yonder sun; or, rather, the law is yonder (sun), and the truth is this (Agni); but, indeed, this Agni is both the one and the other: hence he says, 'the law--the truth, the law--the truth.' He thereby equips him with the he-goat