Śatapatha Brāhmaṇa ("of a hundred paths") 7.5.2.13

7.5.2.13

atha puruṣaśīrṣamudgṛhṇāti | mahayatyevainadetatsahasradā asi sahasrāya tveti sarvaṃ vai sahasraṃ sarvasya dātāsi sarvasmai tvetyetat

He then lifts up the human head--he thereby exalts it--with, 'Giver of a thousand thou art: for a thousand thee!' a thousand means everything: thus, 'the giver of everything, for everything (I bestow) thee!'