Kauṣītaki (Śāṅkhāyana) Brāhmaṇa 3.3.12

3.3.12

dvayam vā idam sarvam chandas kṛtam ca acchandas kṛtam ca /

ficer, it is because the gods do not eat the oblation of one who has not descent from a Ṛṣi. Therefore he utters his descent from a Ṛṣi. He connects the address of fifteen elements; it is the Nivid of the kindling verses; therefore has it fifteen elements; for the kindling verses are fifteen. It is not in metre; all this is twofold, metrical and not in metre; (he says it thinking), ‘With all this let me praise Agni.’ Having connected seven elements he should stop; the metres are seven; verily (they serve) to obtain all the metres. Then (come) four, then four; all this is fourfold; verily (they serve) to obtain all this.