Śatapatha Brāhmaṇa ("of a hundred paths") 11.5.2.7

11.5.2.7

tāni vā etāni cāturmāsyāni triṣaṃdhīni dvisamastāni tasmādimāni puruṣasyāṅgāni triṣaṃdhīni dvisamastāni teṣāṃ vai caturṇāṃ dvayostrīṇi-trīṇi havīṃṣyaniruktāni bhavanti dve-dve dvayoḥ

Now these Seasonal offerings are tripartite and furnished with two joints, whence these limbs of man are tripartite and furnished with two joints. Two of these four (sacrifices) have each three indistinct (low-voiced) oblations; and two of them have two each.