SB 3.12.45
tasyosnig asil lomabhyo
gayatri ca tvaco vibhoh
tristum mamsat snuto ’nustub
jagaty asthnah prajapateh
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Thereafter the art of literary expression, usnik, was generated from the hairs on the body of the almighty Prajapati. The principal Vedic hymn, gayatri, was generated from the skin, tristup from the flesh, anustup from the veins, and jagati from the bones of the lord of the living entities.