Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
Muslims and Christians serve the same God, Allah, but Muslims believe that Allah is the One Who has no partner nor anyone or anything resembles Him, whereas some Christians believe in trinity; embodying God in three shapes; Father, Son, Holy Ghost, which is totally unacceptable in the Islamic creed.
In his response to your question, Sheikh Muhammad Nur Abdullah, President of the Islamic Society of North America (ISNA) and member of the Fiqh Council of North America, states:
It goes without saying that Muslims and Christians are servants of the same Almighty God. However, our belief as Muslims in God is different from our fellow Christians or Catholic. We believe that God is One, with no partners, He does not beget nor was he begotten and there is no one equal to him.
The use of the word God is valid for both Muslims and Christians. Christians of Arab origin refer to God with the Arabic word “Allah” as well as Muslims.
Allah Almighty knows best.
Editor’s note: This fatwa is from Ask the Scholar’s archive and was originally published at an earlier date.