Shatapatha Brahmana 2.6.1.15

2.6.1.15

atha saṃnahanamanuvisraṃsya | apasalavi triḥ paristṛṇanparyeti so 'pasalavi triḥ paristīrya yāvatprastarabhājanaṃ tāvatpariśinaṣṭyatha punaḥ prasalavi triḥ paryeti yatpunaḥ prasalavi triḥ paryeti tadyānevāmūṃstrayānpitṝnanvavāgāttebhya evaitatpunarapodetīmaṃ svaṃ lokamabhi tasmātpunaḥ prasalavi triḥ paryeti

After undoing the band, he moves thrice round from right to left, spreading the sacrificial grass all over (the altar); while spreading it all over from right to left in three layers, he reserves as much as may serve for the prastara-bunch. He then moves again thrice round (the altar) from left to right. The reason why he again moves thrice round from left to right, is that, while the first time he went away from here after those three ancestors of his, he now cones back again from them to this, his own world: that is why he again moves thrice round from left to right.