I had this same conversation in Egypt some years ago. Our Egyptian driver insisted Christians, Jews and Muslims worship the same God. I asked if Muslims believed Jesus Christ died on the cross for our sins. He was silent. I explained Jesus Christ provides our Salvation, and Christians and Muslims don't worship the same God. Allah is not YAHWEH, he is the ancient moon god of the Arab people. And since Allah had no son, how can Christians and Muslims worship the same God? Excellent video here.