Śatapatha Brāhmaṇa ("of a hundred paths") 5.1.3.4

5.1.3.4

tasyā āvṛt | yatra hotā māhendraṃ grahamanuśaṃsati tadasyai vapayā pracareyureṣa vā indrasya niṣkevalyo graho yanmāhendro 'pyasyaitanniṣkevalyameva stotraṃ niṣkevalyaṃ śastramindro vai yajamānastanmadhyata evaitadyajamāne vīryaṃ dadhāti tasmādasyā atra vapayā pracareyuḥ

The course of procedure thereof (is as follows). When the Hotri recites after the Mâhendra libation, then let them proceed with (the offering of) her omentum, for that, the Mâhendra, is Indra's special (nishkevalya) libation; and his also are the Nishkevalya-stotra and Nishkevalya-sastra. Now the sacrificer is Indra: thus he thereby puts strength into the sacrificer in the very middle (of the sacrifice): that is why they should proceed with her omentum at that particular time.