Du'a is an Arabic ( ) term which means to 'call out' or to 'summon'. Muslims use this term and call out to God, and Muslims regard this as one of the greatest acts of worship in Islam. The Prophet Muhammad sal Allahu Alayhi Wa Sallam said "Dua is the very essence of worship." God has commanded Muslims in the Quran to call out to him, citing Surah Ghafir Verse 60:
"And your Lord says: "Call on Me; I will answer your (Prayer): but those who are too arrogant to serve Me will surely find themselves in Hell - in humiliation!" 
The Qur'an ("Qor-Ann") is a Message from Allah to humanity. It was transmitted to us in a chain starting from the Almighty Himself (swt) to the angel Gabriel to the Prophet Muhammad (saas). This message was given to the Prophet (saas) in pieces over a period spanning approximately 23 years (610 CE to 622 CE). The Prophet (saas) was 40 years old when the Qur'an began to be revealed to him, and he was 63 when the revelation was completed. The language of the original message was Arabic, but it has been translated into many other languages.
The Qur'an is one leg of two which form the basis of Islam. The second leg is the Sunnah of the Prophet (saas). What makes the Qur'an different from the Sunnah is primarily its form. Unlike the Sunnah, the Qur'an is quite literally the Word of Allah, whereas the Sunnah was inspired by Allah but the wording and actions are the Prophet's. The Qur'an has not been expressed using any human's words. Its wording is letter for letter fixed by no one but Allah.
Prophet Muhammad (saas) was the final Messenger of Allah to humanity, and therefore the Qur'an is the last Message which Allah has sent to us. Its predecessors such as the Torah, Psalms, and Gospels have all been superceded. It is an obligation - and blessing - for all who hear of the Qur'an and Islam to investigate it and evaluate it for themselves. Allah has guaranteed that He will protect the Qur'an from human tampering, and today's readers can find exact copies of it all over the world. The Qur'an of today is the same as the Qur'an revealed to Muhammad (saas).
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