Narayana Sūkta.10

tiryagūrdhvamadhaśśāyī raśmayaḥ tasya santatā। santāpayati svaṁ dēhamāpādatalamāstakaḥ। tasya madhyē vahniśikhā aṇīyōrdhvā vyavasthitāḥ॥

Staying there, continually spreading his radiance horizontally and vertically, He warms the whole body from the soles of the feet to the crown of the head. At its centre, in its minute form, is the flame of fire, going upward, that is well stationed.