How did Imam Ali Ibn Al-Hussain, Al-Sajjad (PBUH), martyr?

Answer

In the name of Allah, he (PBUH) martyred by poison by Banu Umayyad, and the details are in the books of those who wrote about his biography, such as the holy late scholar Sheikh Baqir Sharif Al-Qurashi and other notable figures (may they rest in peace). Allah knows best.