Is it true that many battles were fought during the reign of Umer bin Khattab but Ali (AS) never took part in any of them? If so, would those battles not be considered as valid Jihad?
Imam Ali (AS) never took part in any matter of the governments of Abu Bakr, Umar and Uthman. He did not attend any Juma or Jama'ah with them (Al-Thahabi in Siyar A'laam al- Nubalaa' 9/284.
Valid Jihad must be led or permitted by the Prophet (SAWA) or his real successors.
Wassalam.