Śatapatha Brāhmaṇa ("of a hundred paths") 13.8.1.19

13.8.1.19

puruṣamātraṃ tveva kuryāt tathāparasmā avakāśaṃ na karoti paścādvarīyaḥ prajā vai paścātprajāmeva tadvarīyasīṃ kuruta uttarato varṣīyaḥ prajā vā uttarā prajāmeva tadvarṣīyasīṃ kurute tadvidhāyāpasalavisṛṣṭābhi spandyābhiḥ paryātanotyapasalavi pitryaṃ hi karma

But let him rather make it just of man's size: he thus leaves no room for another;--broader (varîyas) behind, for what is (left) behind is offspring: he thus makes the (dead man's) offspring more excellent (varîyas);--and broader on the left (north or higher, uttara) side, for the later (uttara) are offspring: he thus makes the offspring more excellent. Having attended to this, he encloses it with cords twisted (and extended) in the non-sunwise way; for the (sacrificial) performance connected with the Fathers is done in the non-sunwise way.