Shatapatha Brahmana 5.5.5.12

5.5.5.12

atho yaḥ sahasraṃ vā bhūyo vā dadyāt | tasya hāpyudavasānīyā syādriricāna iva vā eṣa bhavati yaḥ sahasraṃ vā bhūyo vā dadātyetadvai sahasraṃ vācaḥ prajātaṃ yadeṣa trayo vedastatsahasreṇa riricānam punarāpyāyayati tasmādu ha tasyāpyudavasānīyā syāt

And also for him who would give (to the priests) a thousand (cows) or more, let this be the completing offering. For he who gives a thousand or more becomes as it were emptied out; and that triple Veda is the thousandfold progeny of Vâk (speech): him who was emptied out he thus fills up again with a thousand; and therefore let it be for him also the completing offering.