Shatapatha Brahmana 5.4.1.17

5.4.1.17

tadyadenamūrdhvabāhumabhiṣiñcati | vīryaṃ vā etadrājanyasya yadbāhū vīryaṃ vā etadapāṃ rasaḥ sambhṛto bhavati yenainametadabhiṣiñcati nenma idaṃ vīryaṃ vīryamapāṃ rasaḥ sambhṛto bāhūvlināditi tasmādenamūrdhvabāhumabhiṣiñcati

And as to why he anoints him (standing) with upstretched arms;--those arms in truth are the Râganya's power, and power also is that collected essence of the waters wherewith he now anoints him: 'Lest that power, the collected essence of the waters, weigh down (paralyze) this power of mine, the arms,' thus he thinks, and therefore he anoints him (standing) with upstretched arms.