Did Islam modify pre-Islamic things? I am asking because there are many things present in Islam that also existed in pre-Islamic Arabia, like the concept of jinn,slavery, and so on. The concept of jinn only existed in Arabia before Islam, and no other people of the world believed in them. So why are there many pre-Islamic Arabian concepts in Islam?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.

There is no doubt that Islam opposed and rectified the false beliefs and deviant corrupt practices of the pre-Islamic era. The scholars wrote books addressing the issues that Islam opposed in particular, the best of which is Imaam Muhammad ibn ʻAbd Al-Wahhaab's book Masaa'il Al-Jaahiliyyah. In it, he underlined more than one hundred and thirty beliefs and practices of the People of the Book and disbelievers from the pre-Islamic era that the Prophet enjoined acting against.

You should know that there are no pre-Islamic Arabian concepts as claimed in the question; any observer can easily reach this conclusion. We do not understand what you mean exactly with the concept of jinn in this context. If you mean the existence of the jinn, then you should know that the jinn truly exist, as clearly stated in the Quran. Allaah, The Exalted, says (what means): {And the jinn We created before from scorching fire.} [Quran 15:27] He also says (what means): {And I did not create the jinn and mankind except to worship Me.} [Quran 51:56] A chapter of the Quran is given the name "Al-Jinn." The fact that the Arabs in the pre-Islamic era believed in the existence of jinn does not mean that Muslims are obliged to deny their existence. Islam does not enjoin acting in opposition to the disbelievers of the pre-Islamic era when it comes to what they had of correct beliefs, refined manners, and noble customs. Rather, Islam enjoins acting in opposition to the disbelievers when it comes to false beliefs and unlawful practices. The claim that non-Arabs in the pre-Islamic era did not believe in the existence of the jinn is false and groundless. In fact, it contradicts the religious texts in this regard; the Quran states that the Jews followed that (magic) which the devils rehearsed to them during the lifetime of Prophet Sulayman (Solomon) .

There is no doubt that Islam enjoins acting contrary to the practices of the disbelievers in the pre-Islamic era pertaining to many of their beliefs regarding the jinn. They believed that the angels are the daughters of Allaah and that the mothers of the angels were the daughters of the elite jinn. Allaah, The Exalted, says (what means): {And they have claimed between Him and the jinn a lineage, but the jinn have already known that they (who made such claims) will be brought to (punishment).} [Quran 37:158]

An example of the false beliefs of the pre-Islamic era that were modified by Islam was seeking refuge with the jinn whenever they (the Arabs) camped during their travels. Allaah, The Exalted, says (what means): {And there were men from mankind who sought refuge in men from the jinn, so they (only) increased them in burden.} [Quran 72:6]

Ibn Katheer wrote, "This was the custom of the Arabs in the pre-Islamic era of ignorance. They used to seek refuge with the leader of the jinn of a particular place so that no harm or evil would afflict them. A man used to set out with his family (on a journey) until he came to a piece of land where he would settle. Then he would say, 'I seek refuge with the master (jinni) of this valley from the jinn from my self, my wealth, my child, or my animals being harmed in it.'"

Islam substituted this with seeking refuge with Allaah, The Exalted. The Prophet said, "Whoever dismounts to rest in a place should say, 'Aʻoothu bikalimaati Allaah at-taammaat min sharri ma khalaq,' (I seek refuge with the complete words of Allaah from the evil of what He created),' (whoever does that) nothing will harm him until he remounts." [Muslim]

As for slavery, Islam adopted a wise and gradual approach to discipline it, organize it, and limit it. The Islamic sharee'ah severely limited the channels in which the number of slaves could multiply and opened doors to free slaves and to eventually end slavery. It set freeing slaves as atonement for sins and certain acts of transgression. The Islamic sharee'ah also preserved and honored the rights of the slaves, which were totally neglected in the pre-Islamic era. Pondering over the provisions in fiqh and hadeeth books that addressed the slavery-related provisions, one can easily realize the refined treatment, kindness, and mercy enjoined towards slaves and how Islam urged the Muslims to free slaves and conditioned acts of worship and rewards for that to such an extent that there is no room to go into details in this fatwa. Please, refer to fataawa 83687 and 84431.

Lastly, we advise the dear questioner to learn more about Islam in order to get to know his religion correctly and be able to correct his image of Islam and refute the misconceptions pertaining to the Islamic sharee'ah and its provisions.

Allaah knows best.