Śatapatha Brāhmaṇa ("of a hundred paths") 1.3.4.4

1.3.4.4

athottaram paridadhāti | mitrāvaruṇau tvottarataḥ paridhattāṃ dhruveṇa dharmaṇā viśvasyāriṣṭyai yajamānasya paridhirasyagniriḍa īḍita ityagnayo hi tasmādāhāgniriḍa īḍita iti

He then lays down the northern one, with the text (ib.), 'May Mitra-Varuna lay thee around in the north with firm law for the security of the All! Thou art a fence to the sacrificer, thou Agni, invoked and worthy of invocation!' They are indeed Agnis, and for that reason he says, 'Agni, invoked and worthy of invocation!'