Shatapatha Brahmana 5.5.4.8

5.5.4.8

indro ha vā īkṣāṃ cakre | idaṃ vai mā somādantaryantīti sa yathā balīyānabalīyasa evamanupahūta eva yo droṇakalaśe śukra āsa tam bhakṣayāṃ cakāra sa hainaṃ jihiṃsa so 'sya viṣvaṅṅeva prāṇebhyo dudrāva mukhāddhaivāsya na dudrāva tasmātprāyaścittirāsa sa yaddhāpi mukhādadroṣyanna haiva prāyaścittirabhaviṣyat

Indra thought within himself: 'There now, they are excluding me from Soma!' and even uninvited he consumed what pure (Soma) there was in the tub, as the stronger (would consume the food) of the weaker. But it hurt him: it flowed in all directions from (the openings of) his vital airs; only from his mouth it did not flow. Hence there was an atonement; but had it flown also from his mouth, then indeed there would have been no atonement.