Ruling by Other than what Allah Revealed

Allah criticizes those who ignore His commandments which include every type of righteous good thing and prohibit every type of evil, but they refer instead to opinions, desires and customs that people themselves invented, all of which have no basis in His dīn. During the time of Jahiliyyah, the people used to abide by the misguidance and ignorance that they invented by sheer opinion and lusts. The Tatar (Mongols) abided by the law that they inherited from their king Genghis Khan who wrote Al-Yasiq for them. This book contains some rulings that were derived from various religions, such as Judaism, Christianity and Islam. Many of these rulings were derived from his own opinion and desires. Later on, these rulings became the followed law among his children, preferring them to the Law of the Book of Allah and the Sunnah of His Messenger ﷺ. Therefore, whoever does this, he is a disbeliever

Qadi ‘Iyad on the Sahabah, the Shari‘ah and Madinah and the Return of Ruling by Islam

“From Abu Hurayra, may Allah be pleased with him, “The one upon whom we ask blessings and peace, said, ‘The Hour shall not take place until Iman returns to take refuge in Madinah just like the snake returning to take refuge in her hole.’ ”Abu Mus‘ab al-Zuhri** said regarding this hadith, ‘By Allah! It shall not return and take refuge but among its true followers and its people who establish it completely and properly and who institute in their lives its various precepts and laws, and who have knowledge of its proper interpretation, establishing firmly its rulings by which it judges.’ ”