Shatapatha Brahmana 4.1.2.24

4.1.2.24

tam pratyākramya sādayati | udānāya tvetyudāno hyasyaiṣa tāni vai saṃspṛṣṭāni sādayati prāṇodānāvevaitatsaṃsparśayati prāṇodānāntsaṃdadhāti

Having returned (to the cart-shed), he deposits that (cup) with, 'Thee for the in-breathing!' for this is indeed his in-breathing. He deposits them so as to touch one another; whereby he makes out-breathing and in-breathing touch one another, joins the out-breathings and in-breathings together.