Śatapatha Brāhmaṇa ("of a hundred paths") 9.3.1.8

9.3.1.8

eka eṣa bhavati | ekamiva hi śiraḥ saptetare saptakapālā yadu vā api bahu kṛtvaḥ sapta-sapta saptaiva tacīrṣaṇyeva tatsapta prāṇāndadhāti

That (Vaisvânara oblation) is a single one, for single, as it were, is the head; the others (viz. the Mârutas) are seven in number, of seven potsherds each; and though 'seven-seven' means 'many times,' here it is only seven: he thus places seven vital airs in the head.