Alsalamu Alaykom 1- A person is considered "mulhed" or atheist if he doesn't believe in God. A person is considred "mushrek" if he associate another god with God. Which sin is considered greater: Atheism or associating partners with God? 2-There were muslims (believers) following the true laws of prophet Jesus PBUH before the advent of prophet Mohamed PBUH. Which Gospel or injil did they follow knowing that the Bible was corrupted at that time? Best Regards

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, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

First of all, you should know that both kinds of persons whom you mentioned are in great danger. However, if we compare between the two, then the person who claims that he does not believe in Allaah and he neither worships Allaah nor any other god, is worse than a Mushrik (i.e. a person who associates partners with Allaah), because a Mushrik worships Allaah but he associates with Him another god. Ibn Taymiyyah stated the same thing as he mentioned that Pharaoh is worse than a Mushrik.

As regards your second question, it is confirmed that some people were following the true religion which ‘Eesa (Jesus) came with, and they did not stray until the advent of Islam. The Prophet, sallallaahu ‘alayhi wa sallam, said: “Allaah looked at the people of the earth and he abominated the Arabs and the non-Arabs amongst them, except some of the people of the Book.” [Muslim]

Therefore, these people were following what was in the Injeel (Gospel) which was revealed on ‘Eesa even though there were other people who forged and falsified this Book.