Shatapatha Brahmana 13.8.1.17

13.8.1.17

athāta āvṛdeva agnividhayāgnicitaḥ śmaśānaṃ karoti yadvai yajamāno'gniṃ cinute'muṣmai tallokāya yajñenātmānaṃ saṃskuruta etadu ha yajñiyaṃ karmāsaṃsthitamā śmaśānakaraṇāttadyadagnividhayāgnicitaḥ śmaśānaṃ karotyagnicityāmeva tatsaṃsthāpayati

Now as to the order of procedure. For an Agnikit (builder of a fire-altar) one makes the tomb after the manner of the fire-altar; for when a Sacrificer builds a fire-altar he thereby constructs for himself by sacrifice a (new) body for yonder world; but that sacrificial performance is not complete until the making of a tomb; and when he makes the tomb of the Agnikit after the manner of the fire-altar, it is thereby he completes the Agnikityâ.