Shatapatha Brahmana 10.2.6.10

10.2.6.10

athādhiyajñam yānamūnekaśatamudbāhūnpuruṣānmimīte sa vidhaikaśatavidhaḥ sa citibhireva saptavidhaḥ ṣaḍṛtavyavatyaścitayo'gnireva saptamī vidhā

Now as to the sacrifice. When he measures out those one hundred and one men (man's lengths) with upstretched arms, that is a one hundred and one-fold (altar) in form, and a sevenfold one in respect of its layers: the layers contain six seasonal (bricks) and the fire (or altar) itself is the seventh form.