Shatapatha Brahmana 9.1.1.29

9.1.1.29

yadvevāha sahasrayojana iti | ayamagniḥ sahasrayojanaṃ na hyetasmāditi netyanyatparamasti tadyadagnau juhoti tadevaiṣāṃ sahasrayojane dhanūṃṣyavatanoti

And, again, as to why he says 'at a thousand leagues,'--a thousand leagues means this Agni (fire-altar), for neither this way nor that way is there any other thing greater than he; and it is when he makes offering in the fire that he unstrings their bows at a thousand leagues.