The Prophet (peace be upon him) invited people to one religion. However, we find that there are four Schools of Jurisprudence led by the Four Grand Jurists:
what is the underlying cause for this disunion?
Praise be to Allah Alone. Peace and blessings be upon our Prophet Muhammad, his family, and companions.
The source of Islamic Law is the Qur'an, while the Sunnah explains the text of the Qur'an. As for the four Imams, they were endowed with deep juristic insight and understanding, each according to his capacity. Each of them had disciples who conveyed the principles of their schools and helped the establishment of these four juristic schools. It should be clear that they are Mujtahids (scholars qualified to exercise juristic effort to infer legal decisions) and are liable to err. However, as a Mujtahid, if he arrives at the right decision, he will get double reward and if he errs in a case, he will be rewarded for the sincere effort and (Part No. 5; Page No. 28) his mistake will be forgiven.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.