Board Thread:Naruto Discussions/@comment-26320638-20150422140407/@comment-6769189-20150423025912

Hagoromo says in 670 that he has gone through time and met other transmigarnts and that Madara was the first to mix the chakras.

To address something quake said a little bit further up, that is the translation I am going off of and "awaken" is referring to the mark on his hand and the Rinnegan. Unless Sasuke always had the seal within him, then "awakening" means he gave it both of those things to him.