Kauṣītaki (Śāṅkhāyana) Brāhmaṇa 6.p35

6.p35

vii. 5. The gods obtained expiration by the introductory sacrifice , breathing out by the concluding sacrifice; verily thus also the sacrificer by the introductory sacrifice obtains expiration and by the concluding sacrifice breathing out; the introductory and concluding sacrifices are expiration and breathing out; therefore those who are priests for the introductory sacrifice should also act for the concluding sacrifice, for expiration and breathing out are alike.