Muslims love to point to verses in the Bible they believe are references to the coming of Muhammad as another prophet of God. They get this idea from several verses in the Qur'an, but in particular Sura 7:157, which mentions "those who follow the Unlettered Prophet [euphemism for Muhammad] whom they find mentioned in their own Scripture - in the law and the Gospel..."
Since the Qur'an says Muhammad's name can be found in the Bible - both Old and New Testament - and since Muslims believe the Qur'an to be God's word and God cannot lie, therefore Muhammad's name must be found in the Bible, both testaments. Muslims have scoured the Bible looking for anything resembling a possible reference to Muhammad. Here is a common they use quite often.