Of primary importance is a concept known as Ecumenical Authority. Ecumenical authority means the power or right to establish doctrine.
Therefore since the bible is God's word, the plain reading of the bible (Sola Scriptura) is an expression of God's Ecumenical Authority.
“What is your source?” “I reject that source,” etc. is a type of logically dishonest debating tactic (i.e. a game) played by people who are not interested in honest debate.
For one, it is the responsibility of each person who is engaging in a debate or discussion for being aware of the basic information about a subject, which includes major sources such as the Bible. This doesn't mean you can (or should) reject a request from someone who is asking you to provide scriptural support. It means that beyond such use as a reference for discussion, it is a dishonest request. People who are asking for the source in order to discredit the point or information you are presenting are playing a game and are not interested in the truth of that statement.
A: I make the claim that two plus two is four.
B: What's your source?
A: A convicted felon told me.
B: I don't accept your source.
When discussing religion, and the Judeo-Christian/Islamic religions in particular, one must understand that the Holy Scriptures have been in the public domain for thousands and thousands of years. It is the responsibility of anyone involved to make themselves aware of the basic information available to them in any kind of discussion or debate, and (especially for extra-biblical sources) it is not acceptable to deny or disparage information purely based on where it came from.