Al-salamu alaykum dear brother, thank you for question.
Please allow me to answer.
The story of Isa ibn Maryam a.s. when he forgave adulterous in bible is a forgery. If you do not believe then watch this:
http://www.bartdehrman.com/books/forged.htmthere is not a single authentic book in bible, all are anonymous!
by the way if this story of Isa ibn Maryam a.s. is true and really happened, then
Isa a.s. broke the laws of Old Testament! Do you think that a prophet can break the law of God? Surely no!
In Misquoting Jesus, Ehrman presents persuasive evidence that the story of the woman taken in adultery (John 7:53-8:12) and the last twelve verses of Mark were not in the original gospels, but added by later scribes.[19] Furthermore, these examples “represent just two out of thousands of places in which the manuscripts of the New Testament came to be changed by scribes.â€[20]
In fact, entire books of the Bible were forged.[21] This doesn’t mean their content is necessarily wrong, but it certainly doesn’t mean it’s right. So which books were forged? Ephesians, Colossians, 2 Thessalonians, 1 and 2 Timothy, Titus, 1 and 2 Peter, and Jude—a whopping nine of the twenty-seven New Testament books and epistles—are to one degree or another suspect.
http://www.leveltruth.com/truetojesus.com/articles.html