Śatapatha Brāhmaṇa ("of a hundred paths") 11.4.2.4

11.4.2.4

athāto dhāraṇasya taddhaitadeke kuśalā manyamānāḥ pragṛhya bāhū srucau dhārayanti na tathā kuryādyo hainaṃ tatra brūyācūlau nvā ayamadhvaryurbāhū akṛta śūlabāhurbhaviṣyatītīśvaro ha tathaiva syādatha haiṣa madhyamaḥ prāṇastasmādu tamupanyacyevaiva dhārayet

Now as to the holding (of the spoons). In this respect, some people, thinking themselves clever, hold the two spoons whilst stretching forward both arms; but let him not do so, for if, in that case, any one were to say of him, 'Surely, this Sacrificer has made two spears of his arms: he will become a spear-holder,' then that would indeed be likely to come to pass. But that (navel is the channel of the) central breathing: let him therefore hold (the spoon) by lowering them to that (breathing).