Śatapatha Brāhmaṇa ("of a hundred paths") 3.6.3.4

3.6.3.4

so 'parāhṇe vediṃ stīrtvā | ardhavratam pradāya samprapadyanta idhmamabhyādadhatyupayamanīrupakalpayantyājyamadhiśrayati srucaḥ sammārṣṭyupasthe rājānaṃ yajamānaḥ kurute 'tha somakrayaṇyai padaṃ jaghanena gārhapatyam parikirati padā vai pratitiṣṭhati pratiṣṭhityā eva

In the afternoon, having covered the altar (with sacrificial grass), and handed (to the sacrificer and his wife) one half of the fast-milk, they enter (the hall), put fire-wood on, and prepare the under-layer (of gravel). He (the Adhvaryu) puts the butter on (the old Gârhapatya), and cleans the spoons. The sacrificer takes the king (Soma) on his lap. He (the Adhvaryu) scatters about the (dust of the) foot-print of the Soma-cow behind the (new) Gârhapatya for the sake of a firm standing, for it is with the foot that one stands firmly.