Allah is in lots of scriptures. The Christian and Jewishs ones for example. The Hebrew for Allah is Eloah. When this is made plural you get Elohim which is used in the Bible a few times for God, e.g. in the Genesis book. The Hindu scriptures may have it, i am not sure. I know that they predict Muhammed, peace and blessings upon him, contain Amina (his mother) and Abduallah (his father). My own theory is their god called Brhama is actually Abraham, peace and blessings upon him. The sikh scriptures contain the word 'Muslim' many times because they were made from Muslims and spiritual people.
'Recently Father Pecerillo, a famous Franciscan Archaeologist, found more than twenty churches in Madaba at the south of Jordan. From the Forth Century we found houses in Syria, Lebanon, Iraq and Palestine with this inscription in Arabic :"Bismi Allah al-Rahman al-Raheem" which shows that even people before Islam used this Holy name, "Allah", for GOD Almighty, which proves that the name of GOD Almighty in the Noble Quran, "Allah", is the correct one. There are still missing pieces in it that disprove trinity.
Further discoveries from an Arabic Roman Catholic website at http://www.al-bushra.org/arbhrtg/arbxtn04.htm:
Recently also, Father Pecerillo, a famous Franciscan Archeologist, found from the Forth Century (200 years before Islam) houses in Syria, Lebanon, Iraq and Palestine with this inscription in Arabic :"Bismi Allah al-Rahman al Raheem" which means in Arabic "In the name of ALLAH, the Most Merciful and the Most Gracious", which again proves that His Holy name existed before Islam'.
As you can see, both the Arab Jews and arab Christians use Allah in their prayers. And it is connected to Elohim.