After Sasuke awakened the Rinnegan, the Sage of Six Paths referred to him as the reincarnation of Indra similarly when he was explaining to others, he referred Madara as Indra's reincarnation, while he was alive and Madara awakened Rinnegan when he was old near to his end. Following the final battle between Naruto and Sasuke, they broke the reincarnation cycle. Still Sasuke is considered as reincarnation of Indra till he die.
ch 0 2 2.Brawl over Body
Anime & Comics · Uday_Adlet
It's a suspense for now. I will write about how they were related in my 7th or 8th chapter. Please read my work and give me comments on where I am lacking. Thank you for comments and replies.
Sasuke : The God of Eternity
Anime & Comics · Uday_Adlet