Essentially, the Shahada is the Islamic creed which declares God's oneness and Muhammad as God's messenger. It literally says, "There is no god but God, and Muhammad is God's messenger." This is very similar to the Jewish Shema from Deuteronomy 6:4, which states, "Hear O Israel, the Lord is our God, the Lord is One." Both affirm the oneness of God. Christianity itself, affirming the Old Testament, agrees to the oneness of God in that there is one God.I have already written about whether or not Allah is the same God as that of Christianity, so I won't go into that here. The Shahada is recited at the beginning of the five daily prayers, by a Muslim who is about to die, and in Arabic for one to convert to Islam. There is some controversy over whether Muslims trick some people into saying it so that they can have converts, but this is not really proven. Christians are accused of the same thing, and we perhaps do in our zeal to get people to say a prayer of "accepting Christ into one's heart."
Christians obviously have a problem with the second half of the creed in it's declaration of Muhammad as a messenger (or prophet) of God. Muslims will claim that Jesus himself prophesied the coming of Muhammad, but this is based on a false assumption of Jesus' prophesy of the Holy Spirit. That, and the Imams leading the Muslims astray on this topic. I've spoken with Muslims in Mali, who claimed this, but were astounded when I showed them what the Bible actually said on the topic. No one had ever bothered to show this to them. They had also been in conversation with the cult group, the Jehovah's Witnesses, in the past.
How do we respond to the Shahada then with the Gospel? Well, must always affirm that there is indeed, one true God. John Chapter 1 is a great place to start in affirming both one God and the oneness of God in his trinitarianism. Now is not the time to bring up the Trinity with a Muslim, but John 1 is a good place to start. We must show from scripture, and again, John 1 is a great place to start. Hebrews greatly helps in showing that Jesus is the greater prophet.
Don't ever, ever proceed to demean Muhammad. Once you go down that road, you've lost practically any chance you may have, apart from intervention through the Holy Spirit, to further witness to the Muslim. Muslims revere both Jesus and Muhammad. Our job is to elevate Jesus. Some Muslim Background Believers have changed the Shahada to reference Jesus, rather than Muhammad, upon conversion. We must be careful with that, to avoid potential syncretistic outcomes.
Just a note that what I'm referencing is orthodox Islam as it relates to the majority of Muslims who are of the Sunni sect. Shi'a and Sufi sects may reference or substitute other prophets with Muhammad in the Shahada. I will detail the different sects in later posts, but I would encourage you to lift up Christ in all that you do in your ministering to Muslims.