Shatapatha Brahmana 3.5.1.34

3.5.1.34

tāṃ vai yugamātrīṃ vā sarvataḥ karoti | yajamānasya vā daśadaśa padāni daśākṣarā vai virāḍvāgvai virāḍvāgyajño madhye nābhikāmiva karoti samānatrāsīno vyāghārayāṇīti

He makes it on each side either of the size of the yoke, or ten feet of the sacrificer's; for the Virâg consists of ten syllables, and the Virâg is speech, and the sacrifice is speech. In the middle he makes, as it were, a navel, thinking, 'Seated in one and the same place, I shall sprinkle (ghee) all round.'