What is the evidence for the prohibition of masturbation in the Qur'an and Sunnah, and is the view of it being reprehensible instead of forbidden correct?

No one is permitted to declare something lawful or unlawful based on their own whim. Rather, the ultimate authority for what is lawful and unlawful belongs to Allah the Almighty, in fulfillment of His saying: "And in whatsoever you differ, its ruling is with Allah." And people of knowledge are too pious to rule according to their own whims.