Śatapatha Brāhmaṇa ("of a hundred paths") 4.5.4.8

4.5.4.8

te māhendrasyaivānu homaṃ hūyante | eṣa vā indrasya niṣkevalyo graho yanmāhendro 'pyasyaitanniṣkevalyameva stotraṃ niṣkevalyaṃ śastramindro vai yajamāno yajamānasya vā ete kāmāya gṛhyante tasmānmāhendrrasyaivānu homaṃ hūyante

They are offered after the offering of the Mâhendra graha; for that, the Mâhendra, is Indra's special cup; and so are the (Nishkevalya) stotra and sastra specially his. But the sacrificer is Indra; and for the sacrificer's benefit (these cups) are drawn: therefore they are offered after the offering of the Mâhendra graha.