I've been listening to a lot of Muslim - Christian debates. Here are three that have interested me recently - each of them with Dr Shabir Ally.
Firstly there's James White vs Shabir Ally on whether the earliest witnesses to Jesus confessed His deity:
White argues that the earliest sources unashamedly confess the deity of Christ - the "Carmen Christi" of Philippians 2, the "NT Shema" of 1 Corinthians 8 and Mark's Gospel speak of Jesus as Yahweh. Fascinatingly Shabir seems to concede as much, at least over the Philippians 2 material, but then claims that this must be a corruption of the earliest beliefs. Why? Because we know that the Jews were monotheists (which Shabir conflates time and again with "unitarians").
Shabir wriggles off the hook because he claims that the Old Testament is unitarian. If this is so then NT trinitarianism must be a corruption and the Quran must be correct in saying that the Christians have changed their book. His wriggling is very unconvincing, obviously, because the evidence James brings is without question the earliest. All Shabir can do is to claim that beneath the Scriptures there must lie an original unitarian faith in Jesus that gets developed in trinitarian ways over time. It's all a "just so story" but he gets away with it because he asserts that the OT is unitarian.
The second debate I watched recently was Jay Smith versus Shabir Ally. Watch Jay's 35 minute opening statement from 17:55 where he brings devastating critiques of the historicity of the Quran and its transmission:
Shabir responds with numerological hocus pocus from 53:45. As Dr Ally waxes lyrical about the number 19 in the Quran your jaw will hit the floor (but not in the way Dr Ally hopes). It's astonishing that this would be put forward in a serious debate and take up so much of Dr Ally's argument. Jay's historical critique of the Quran remains completely unanswered.
But still Shabir wriggles off the hook because, well, we all know that the NT must be corrupt? Why? Because it changes the doctrine of God from the OT.
Ok then, step forward Nabeel Qureshi. I loved this debate. Just listen to Nabeel's opening statement from 8:15.
Here Nabeel is hitting where it hurts. I love that he questions whether Tawhid (Islam's unitarianism) is the simple doctrine of God that Muslims claim. Actually Tawhid involves Muslims in all sorts of difficulties. If Allah is alone, how can he break free from the prison of his own transcendence to communicate with creatures. Some Muslims speak of the word of Allah existing with him in eternity which is really the only way you could have true revelation from Allah. Only if the Quran is an eternal communication could it communicate the eternal God. But of course as soon as you say that you are threatening Tawhid because you have something alongside Allah.
In Christian theology the eternal Word who is God from God is not a problem. He's the solution. Without Him God must be mute and we must be left in the dark. Nabeel was right to press Shabir on the question of the Quran's eternality, it goes to the heart of the Islamic doctrine of God and forces the Muslim to the horns of a dilemma. Either God does not have an eternal word and thus we cannot know that Allah is transcendent or he does have an eternal word and Tawhid is completely compromised.
More fundamentally though Nabeel establishes that the OT, in its own context and on its own terms, is not unitarian at all and could not be read unitarianly. This is where I have found evangelism to Muslims gaining most traction. When you show that Yahweh is face to face with Abraham and then rains down judgement from the-LORD-out-of-the-heavens (Genesis 18:1; 19:24) you show that Moses' doctrine of God is nothing like Mohammed's.
Have a watch and enjoy Nabeel's arguments. And if you want another couple dozen more OT Scriptures - see these 24 verses that cannot be read unitarianly in the Hebrew Bible. We simply do not see a progression from unitarianism to trinitarianism in the Bible or history. What we see in the Scriptures is a compound unity to God with three Persons who may take divine titles. We see this from Genesis 1 onwards. Unitarianism is not the pure origin, it is the much later corruption. This corruption began with the Rabbis reacting against the early Christians and continued with the heresy of Islam (much aided by pagan philosophy).
One thing I admire about Islam is its comprehensive view of history. For them Adam is a Muslim, so is Moses, so is Jesus - and they all taught Tawhid. The Christian view of history ought to be similarly consistent. Adam is a Christian, so is Moses, so are all true prophets - and they were all trinitarian. These are the arguments that truly fight fire with fire in Muslim-Christian debate and these are the truths that make sense of our Christian faith: triune from the beginning.