My friend attacked with Colossus of Akros (Monstrous 20/20 indestructible) and I blocked with my Xenagos, God of Revels (6/5 indestructible). I believe that our creatures are safe since indestructible prevents them from dying by combat damage.
My friend though believes that the indestructible ability would cancel each other out and his Colossus would destroy my Xenagos. Are there any rules that explains what happens in this situation?