1500 B.C.
"The revealed scriptures, like Manu-samhita and similar others, are considered the standard books to be followed by human society. Thus the leader's teaching should be based on the principles of such standard sastras. One who desires to improve himself must follow the standard rules
as they are practiced by the great teachers.""Bhagavad-Gita As It Is", 3.21 Purport
His Divine Grace A.C. Bhaktivedanta Swami Prabhupada