With all due respect that's begging the question.
It's you Protestants that demand we Catholics "show that in Scripture" and then turn around and say that if we demonstrate something in Scripture, that "proves scripture trumps tradition"? Really?
This is actually why I personally never play this "show me from scripture" game anymore (other than to demonstrate on occasion there are alternate ways to read Scripture than the Protestant way). Because it's ultimately your burden to demonstrate Scripture is the only source of moral certainty for a Christian, because such a way of thinking was unheard of before the "Reformation".
See #247 for starters. And that's only the tip of the iceberg.
But you may be partially correct, for though such ways of thinking were once prevalent within the wider, catholic thus universal Church, in the Western Church (entirely dominated by the Church of Rome) prior to the Reformation that tradition had been superseded by sola ecclesia (whatever we say) by those of the Church of Rome.
Like a monkey with an arm in jar having a narrow opening, and it's paw around a nut it is convinced it just has to have -- the RCC is still captured by it's own desires to be the place having the bishop of bishops and supremacy over and above Scripture when the scriptures are inconvenient to the desire.
...”demonstrate Scripture is the only source of moral certainty for a Christian”.......
If the Bible isnt the Christians source for morality, then What should be?
My view is based on the fact God exists and is our creator who has spoken to us in His written word.... So if this isn’t the starting point then we’re just like anyone else trying to find objectivity in a sea of subjectivity.
We also have our conscience (another source), but that is only as good as the moral standard ‘that informs it’.... If its not the Bible, then we inform our conscience by other means...such as social morality.... which becomes shaped and ‘changed’ by the culture around us (cultural relativism)....and that is always “shifting sand”......Everyone did what was right in his own eyes (Judges 17:6)
Therefore there must be a final absolute authority to which we can stand on...... “Forever, O Lord, your word is settled in heaven “ (Psalm 119:89)....
You have sources to substantiate THAT claim?