Because that Abraham obeyed my voice, and kept my charge, my commandments, my statutes, and my laws. Genesis 26:5
"The brevity of the record in Genesis causes us to overlook many facts of the deepest interest. 
Adam lived 930 years. How deep and absorbing the interest that must have existed in the human family to see the first man! To converse with one who had himself talked with God! To hear from his lips a description of that Paradise in which he had lived! To learn from one created on the sixth day the wondrous events of the creation week! To hear from his lips the very words of the Creator when he set apart his rest-day to a holy use! And to learn, alas! the sad story of the loss of Paradise and the tree of life!
It was therefore not difficult for the facts respecting the six days of creation and the sanctification of the rest-day to be diffused among mankind in the patriarchal age.
Nay, it was impossible that it should be otherwise, especially among the godly. From Adam to Abraham a succession of men probably inspired of God preserved the knowledge of God upon earth.
*Thus Adam lived till Lamech, the father of Noah, was 56 years of age; Lamech lived till Shem, the son of Noah, was 93; Shem lived till Abraham was 150 years of age.
Thus are we brought down to Abraham, the father of the faithful. Of him it is recorded that he obeyed God's voice and kept his charge, his commandments, his statutes and his laws." J.N. Andrews