Śatapatha Brāhmaṇa ("of a hundred paths") 11.6.2.3

11.6.2.3

atha hovāca śomaśuṣmaḥ sātyayajñiḥ teja eva samrāḍahaṃ tejasi juhomīti kathaṃ tadityādityo vai tejastaṃ sāyamagnau juhomyagnirvai tejastam prātarāditye juhomīti kiṃ sa bhavati ya evaṃ juhotīti tejasvī yaśasvyannādo bhavatyetayoścaiva devatayoḥ sāyujyaṃ salokatāṃ jayatīti

Then Somasushma Sâtyayagñi said, 'I, O king, make offering to light in light.'--'How is that?' asked the king.--'Well, Âditya is light: to him I make offering in Agni in the evening; and Agni, indeed, is light: to him I make offering in Âditya in the morning.'--'What becomes of him who offers in this way? He verily becomes lightsome, and glorious, and prosperous; and attains to the fellowship of those two deities, and to an abode in their world.'