Originally Posted by DRAGONBPY
@Gamabunta. After Madara gave his eyes to Nagato, Nagato may have unlocked rinnegan. Kabuto modified Madara so he was in his prime. he may have also modified Madara so that he received the eyes that Nagato unlocked hence giving him Rinnegan.
Ok so kabuto do some experimental stuff with Edo-Madara eyes with uzumaki dna to enable Edo-Madara to have the rinnegan.
So my next question is how then Madara knew about rinne tensei if he wasn't the one who awaken rinnegan and learned what it can do.