One of the common mistakes people make when comparing Christianity and Islam is assuming that they share the same god, just different ways. People assume this because they both trace back to Jewish roots, and bleing to the Abrahamic religions. t Christianity, Islam, and Judaism are called the Abrahamic religions, which means they attribute the beginning of their history to the revelation of God to Abraham (read more about Abrahamic Religions).
Though Islam connects their god to being the creator, the one who called Abraham and sent Moses, the attributes of their god, Allah, differs greatly from how God reveals Himself in the Bible. Based one this, we can say that Christianity and Islam do not present the same god. Islam has taken the idea of the Judeo-Christian God, the true God, and warped it to fit into Arabic tribal religious practice and politics. We're going to break down the differences between Yahweh and Allah), and then we'll understand why it's so important to emphasize that the Christian God is nothing like Allah.
The Basic Differences
Name
First, God goes by a different name than what the Islamic god goes by. Yahweh is the intimate name of God in the Bible, and was originally only supposed to be uttered by the high priest. Under the new covenant with Jesus, we do not need priests to communicate with God s; we are able to call Him by his personal name, because our relationship with Him is personal. God is also known as "I AM WHO I AM", which is the name He gave to Moses when he was sent to free Israel from Egypt.
Islam's god goes by "Allah".. The name "Allah" is an abbreviation of the Arabic word "Al-ilah" which directly translates to "the god."
Character
The character of Allah is also in conflict with Yahweh's character. While Yahweh is consistent, loving, and honest, Allah's commands directly contradict themselves, they change over time, and he does not condemn lying in many situations
Consistency
Matthew 24:35 tells us that "Heaven and earth will pass away, but My words will not pass away." God's words to us are consistent and cannot be changed or negated.
However, the Quran tells us in 2:106 that "None of our revelations do we abrogate or cause to be forgotten but We substitute something better or similar - knowest thou not that Allah has power over all things?" If Allah was the true god, then he would not need to replace what he had originally said with "better" things.
Honesty
God is unable to commit evil or tempt anyone (James 1:13), but Allah is considered "the best of schemers [deceivers]" according to Quran 3:54.
Love
God is love. He loves all of his creation, whether they follow Him or not. "The one who does not love does not know God, for God is love. By this the love of God was manifested [a]in us, that God has sent His [b]only begotten Son into the world so that we might live through Him. In this is love, not that we loved God, but that He loved us and sent His Son to be the propitiation for our sins." 1 John 4:8-10.
Allah only "likes" devout Muslims. He is affectionate to them. This means that one must earn Allah's approval, by being a devout slave (Quran 85:13, Quran 2:195).
Relationship to Us
Finally, the relationship that Yahweh desires to have with us is nothing like what Allah demands from his followers. Yahweh has called us to be His children: "But as many as received Him, to them He gave the right to become children of God, even to those who believe in His name" - John 1:12 NASB. However, Allah wants his followers to submit to him like slaves who are afraid of their master.
So if you're ever talking to a Muslim friend, and they are assuming that you both worship the same God, you can ask them these questions to help them realize the differences between Allah and the true God:
The Bible says that God is incapable of doing evil. What does the Quran say about Allah?
 I believe that God's word never changes. I've heard that Allah changes what he says and improves on what he previously said. If he was God, then why would he need to correct himself?
I've heard that Allah only loves devout Muslims. The God of the Bible loves me and everyone unconditionally. Would you like to hear more about Him?
Ultimately, the thing that sets God apart from Allah is His love, so when you're talking to your Muslim friends about Him, that is the main thing to offer to them: a loving relationship with a Father who will never desert them.