Aitareyabrahmana 2.2.p12

2.2.p12

now as to his reciting before the speaking of the fowls (it is because they think), 'Let us not speak after speech has been uttered unconnected with the sacrifice.' Therefore it should be recited in the deep of the night. Or rather when the Adhvaryu begins, then he should recite; when the Adhvaryu begins, verily with speech he begins, at speech the Hotṛ recites, for speech is the holy power. Herein is the desire obtained which is in speech and in the holy power.