[ALLAH’S Quran – 9:31] “They have taken as lords beside Allah their rabbis and their monks and the Messiah son of Mary when they were bidden to worship only One Allah. There is no Allah save Him. Be He Glorified from all that they ascribe as partner (unto Him)!
The Prophet (Peace Be Upon Him) has said : [Bukhari, Book 78, Hadith 8] Narrated Anas bin Malik: Allah’s Messenger (PBUH) mentioned the greatest sins or he was asked about the greatest sins. He said, “To join partners in worship with Allah; to kill a soul which Allah has forbidden to kill, and to be undutiful or unkind to one’s parents.” The Prophet (PBUH) added, “Shall I inform you of the biggest of the great sins? That is the forged statement or the false witness.” Shu`ba (the sub-narrator) states that most probably the Prophet said, “the false witness.”