Allah (The one and only true God)

In Islam:

In Islam, Allah is the unique, omnipotent and only deity and creator of the universe.

According to Islamic belief, Allah is the most common word to represent God, and humble submission to HIS will, divine ordinances and commandments is the pivot of the Muslim faith. "He is the only God, creator of the universe, and the judge of humankind." "He is unique (wāḥid) and inherently one (aḥad), all-merciful and omnipotent." The Qur'an declares "the reality of Allah, His inaccessible mystery, His various names, and His actions on behalf of His creatures."

In Islamic tradition, there are 99 Names of God (al-asmā’ al-ḥusná. meaning: 'the best names' or 'the most beautiful names'), each of which evoke a distinct characteristic of Allah. All these names refer to Allah, the supreme and all-comprehensive divine name. Among the 99 names of God, the most famous and most frequent of these names are "the Merciful" (al-Raḥmān) and "the Compassionate" (al-Raḥīm).

Most Muslims use the untranslated Arabic phrase in shā’ Allāh (meaning 'if Allah wills') after references to future events. Muslim discursive piety encourages beginning things with the invocation of bismillāh (meaning 'in the name of Allah).

There are certain phrases in praise of God that are favored by Muslims, including "Subḥān Allāh" (Holiness be to Allah), "al-ḥamdu lillāh" (Praise be to Allah), "lā ilāha illā Allāh" (There is no deity but Allah) and "Allāhu akbar" (Allah is greatest) as a devotional exercise of remembering God (dhikr).

In Christianity:

The Aramaic word for "God" in the language of Assyrian Christians is ʼĔlāhā, or Alaha. Arabic-speakers of all Abrahamic faiths, including Christians and Jews, use the word "Allah" to mean "God". The Christian Arabs of today have no other word for "God" than "Allah". (Even the Arabic-descended Maltese language of Malta, whose population is almost entirely Roman Catholic, uses Alla for "God".)

Some archaeological excavation quests have led to the discovery of ancient pre-Islamic inscriptions and tombs made by Arab Christians in the ruins of a church at Umm el-Jimal in Northern Jordan, which contained references to Allah as the proper name of God, and some of the graves contained names such as "Abd Allah" which means "the servant/slave of Allah".

The name Allah can be found countless times in the reports and the lists of names of Christian martyrs in South Arabia, as reported by antique Syriac documents of the names of those martyrs from the era of the Himyarite and Aksumite kingdoms

A Christian leader named Abd Allah ibn Abu Bakr ibn Muhammad was martyred in Najran in 523, as he had worn a ring that said "Allah is my lord".
In an inscription of Christian martyrion dated back to 512, references to Allah can be found in both Arabic and Aramaic, which called him "Allah" and "Alaha", and the inscription starts with the statement "By the Help of Allah".

In pre-Islamic Gospels, the name used for God was "Allah", as evidenced by some discovered Arabic versions of the New Testament written by Arab Christians during the pre-Islamic era in Northern and Southern Arabia.
Pre-Islamic Arab Christians have been reported to have raised the battle cry "Ya La Ibad Allah" (O slaves of Allah) to invoke each other into battle.

"Allah" was also mentioned in pre-Islamic Christian poems by some Ghassanid and Tanukhid poets in Syria and Northern Arabia.

In Malaysian and Indonesian language:

Christians in Malaysia and Indonesia use Allah to refer to God in the Malaysian and Indonesian languages (both of them standardized forms of the Malay language). Mainstream Bible translations in the language use Allah as the translation of Hebrew Elohim (translated in English Bibles as "God"). This goes back to early translation work by Francis Xavier in the 16th century. The first dictionary of Dutch-Malay by Albert Cornelius Ruyl, Justus Heurnius, and Caspar Wiltens in 1650 (revised edition from 1623 edition and 1631 Latin edition) recorded "Allah" as the translation of the Dutch word "Godt". Ruyl also translated the Gospel of Matthew in 1612 into the Malay language (an early Bible translation into a non-European language made a year after the publication of the King James Version which was printed in the Netherlands in 1629. Then he translated the Gospel of Mark, published in 1638.

The government of Malaysia in 2007 outlawed usage of the term Allah in any other but Muslim contexts, but the Malayan High Court in 2009 revoked the law, ruling it unconstitutional. While Allah had been used for the Christian God in Malay for more than four centuries, the contemporary controversy was triggered by usage of Allah by the Roman Catholic newspaper The Herald. The government appealed the court ruling, and the High Court suspended implementation of its verdict until the hearing of the appeal. In October 2013 the court ruled in favor of the government's ban. In early 2014 the Malaysian government confiscated more than 300 bibles for using the word to refer to the Christian God in Peninsular Malaysia. However, the use of Allah is not prohibited in the two Malaysian states of Sabah and Sarawak. The main reason it is not prohibited in these two states is that usage has been long-established and local Alkitab (Bibles) have been widely distributed freely in East Malaysia without restrictions for years. Both states also do not have similar Islamic state laws as those in West Malaysia.