The bible doesn't specifically mention abortion being wrong. It seems like it should if the bible truly is anti-abortion since according to Wikipedia (link below) the first recorded evidence of induced abortion is from the Egyptian Ebers Papyrus in 1550 B.C., making it something that would be known to exist back in biblical times.
Most religious people who cite the bible as being against abortion deduce it from various passages which refer to life and the mother's womb. This argument is in some ways similar to how the U.S. Constitution is silent on "innocent until proven guilty" but it has been deduced by the courts from what the U.S. Constitution does say about criminal proceedings.
https://en.wikipedia.org/wiki/History_of_abortion