Namaste, It is paingarAhasya brAhmaNa which is the brAhmaNa bhAga of Rg Veda. There are 4 brAhmaNa bhAgAs of Rg Veda: 1) aitrEya 2) shAnkhyAyana (kauSitaki) 3) paingirAhasya 4) sAtyAyana Among the 4 above, only aitrEya & kauSitaki are available now. Rest are lost. regs, sriram