Full Idea
Aristotle goes to great lengths to defend the principle of non-contradiction, and does not at all think that it is obviously true.
Gist of Idea
Aristotle does not take the principle of non-contradiction for granted
Source
report of Aristotle (Metaphysics [c.324 BCE], logic) by Vassilis Politis - Aristotle and the Metaphysics 5.1
Book Reference
Politis,Vasilis: 'Aristotle and the Metaphysics' [Routledge 2004], p.125