Adjective : an unquestionable fact. ,a man of unquestionable principles.    From Dictionary.com. 

Moreover, the greatest care was taken to impress students with the unquestionableness of Protestant orthodoxy, especially the doctrines of Christ's deity and his substitutionary sacrifice, of human depravity, miraculous grace, and future punishment.    From Wordnik.com.  [The Theology of Schleiermacher: A Condensed Presentation of His Chief Work, "The Christian Faith"] Reference