Shatapatha Brahmana 5.2.5.11

5.2.5.11

atha yadaindrāsaumyaḥ | carurbhavatīndro vai yajamāno varcaḥ somaḥ sa yadevāsmā agnirdātā varco dadāti tenaivaitatsaṃspṛśate tadānmankurute

And as to why there is a pap for Indra and Soma;--Indra is the Sacrificer, and Soma is glory: whatever glory Agni, the giver, gives him, therewith he now puts himself in contact, that he makes his own.