Aitareyabrahmana 7.21

7.21

athāta iṣṭāpūrtasyāparijyāniḥ kṣatriyasya yajamānasya.
sa purastād dīkṣāyā āhutiṃ juhuyāc caturgṛhītam
ājyam āhavanīya iṣṭāpūrtasyāparijyānyai
punar na indro maghavā dadātu \ brahma punar iṣṭam pūrtaṃ dāt svāhety
athānūbandhyāyai samiṣṭayajuṣām upariṣṭāt:
punar no agnir jātavedā dadātu \ kṣatram punar iṣṭam pūrtaṃ dāt svāheti
saiṣeṣṭāpūrtasyāparijyāniḥ kṣatriyasya yajamānasya yad ete āhutī,
tasmād ete hotavye

vii. 21 (xxxiv. 3). Then comes the prevention of decay of the sacrifice and the gifts (to the priests) for a Kṣatriya as sacrificer. Before the consecration he should offer a libation of butter in four portions, in the Āhavanīya to prevent the decay of the sacrifice and the gifts, with

'Let Indra, the bounteous, restore to us
The holy power; let him give again the sacrifice, the gifts; hail!'

Then after the concluding formulas of the final offering of a cow ‘Let Agni, all knower, restore to us The lordly power; let him give again the sacrifice, the gifts; hail!’ These two libations are the prevention of decay of the sacrifice and the gifts for a Kṣatriya as sacrificer; therefore should they be offered.