The title say it all.
Madara have faught the senju clan many times in his life time.If he already knew that Rinnegan require senju dna he could take any random senju member dna and obtain Rinnegan.
Probably i believe the battle between Madara and hashimara was planned out by Madara because he had many option to get rinnegan .Madara did not actually lost the battle because still end up being alive afterwards
Madara have faught the senju clan many times in his life time.If he already knew that Rinnegan require senju dna he could take any random senju member dna and obtain Rinnegan.
Probably i believe the battle between Madara and hashimara was planned out by Madara because he had many option to get rinnegan .Madara did not actually lost the battle because still end up being alive afterwards