Shatapatha Brahmana 13.1.7.2

13.1.7.2

apa vā etebhyaḥ prāṇāḥ krāmanti ye dīkṣāmatirecayanti saptāham pracaranti sapta vai śīrṣaṇyāḥ prāṇāḥ prāṇā dīkṣā prāṇairevāsmai prāṇāndīkṣāmavarunddhe tredhā vibhajya devatāṃ juhoti tryāvṛto vai devāstryāvṛta ime lokā ṛddhyāmeva vīrya eṣu lokeṣu pratitiṣṭhati

But, indeed, the vital airs depart from those who exceed (the duration of) the Dîkshâ. For seven days they observe it; for there are seven (outlets of) vital airs in the head, and the Dîkshâ is the vital airs: it is by means of the vital airs he gains the Dîkshâ, the vital airs, for him. He makes offering by dividing (each) deity into three parts; for the gods are of three orders, and of three orders are these worlds: he thus establishes himself in these worlds in prosperity and vital power.