Hazrat Umar [RA] said if anybody without the consent of Muslims tries to become ruler of the Muslim, kill him. Not only that he (R.A) banned his son (R.A) from contesting for the position of Caliph. [AL-TABARI PAGE 292, IBN- ALASEER PAGE 34-35-IDARAT –UL- TABAT-AL-MUNIRIYA-EGYPT]
Same as Imam Hussain R.A struggled for the cause to save Islamic Govt and its ethics from the unjust ruler Yazeed.
Due to subdued sound quality. Reference to the book 'Al-Jihad wa'l Qital fi as-Siyasa ash-Shar'iyya' is given here.This three volume book is the work of Sheikh Dr. Muhammad Khayr Haykal which was his PhD thesis from the University of Damascus, Syria.
This book covers many issues related to Jihad and fighting, but its primary focus is the Jihad and fighting that will be performed by a future Khilafah.
