Shatapatha Brahmana 14.2.1.14

14.2.1.14

atha vipruṣo'bhimantrayate svāhendravatsvāhendravaditīndro vai yajñasya devatā sā yaiva yajñasya devatā tāmevaitatprīṇāti tasmādāha svāhendravatsvāhendravaditi triṣkṛtva āha trivṛddhi yajño'varaṃ svāhākāraṃ karoti parāṃ devatāmasāveva bandhuḥ

The (spilt) drops he then consecrates with, 'Hail, possessed of Indra! hail, possessed of Indra!' for Indra is the deity of the sacrifice: he thus pleases him who is the deity of the sacrifice, and therefore he says, 'Hail, possessed of Indra! hail, possessed of Indra!' Thrice he says it, for threefold is the sacrifice. The call of 'hail!' he places first, and the deity last: the significance of this is the same as before.