Matsya Purana 58.9

58.9

nava saptārtha vā pañca nātiriktā nṛpātmaja!.
vitastimātrā yoniḥ syāt ṣaṭ‌saptāṅgulivistṛtā.. 58.8 ..

A pandal (maṇḍapa), measuring sixteen hands, with four openings should also be made, and then around the altar should be made pits (gartas), five, seven or nine, but not more in number, one cubit deep and three circles round them. The receptacle (yoni) of the altar should be one span long and six or seven fingers broad.—7-8.