Shatapatha Brahmana 11.7.2.5

11.7.2.5

itthameva kuryāt puroḍāśeḍāyāmevopahūtāyāṃ dakṣiṇā nayedaindro vā ayam madhyataḥ prāṇa imamevaitadaindram madhyataḥ prāṇaṃ dakṣiṇābhirdakṣayatyaindraṃ vai mādhyandinaṃ savanam mādhyandine vai savane dakṣiṇā nīyante tasmātpuroḍāśeḍāyāmevopahūtāyāṃ dakṣiṇā nayet

Let him perform it in this way:--when the Idâ of the cake-offering has been invoked, he should bring up the Dakshinâs; for to Indra belongs this vital air in the centre (of the body): by means of the Dakshinâs he thus strengthens this vital air in the centre (of the body); and to Indra also belongs the midday Soma-service, and at the midday-service the Dakshinâs are brought up: therefore. he should bring up the Dakshinâs after the invocation of the Idâ of the cake-offering.