SB 4.21.18
vyañjitasesa-gatra-srir
niyame nyasta-bhusanah
krsnajina-dharah sriman
kusa-panih krtocitah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
As Maharaja Prthu was being initiated to perform the sacrifice, he had to leave aside his valuable dress, and therefore his natural bodily beauty was visible. It was very pleasing to see him put on a black deerskin and wear a ring of kusa grass on his finger, for this increased the natural beauty of his body. It appears that Maharaja Prthu observed all the regulative principles before he performed the sacrifice.