Christianity and Islam are both born out of Judaism and they basically share the same texts up until Abraham. Beyond that they also recognise common prophets, with Jesus viewed as a prophet of God by both Jews and Muslims but as his son by Christians.
So, for example, because all three religions recognise Jesus as proclaiming the word of God, they must therefore be working from a common view of who or what 'God' is, irrespective of what name they attribute to him.
Given, though, that 'God' is a totally mythical figure anyway, there is obviously scope for some variation in how people see him!