How did Imam Ali AsSajjad and Lady Zainab passed away? I read a commentary that they were assassinated. When and who killed them?

Imam Al-Sajjad was poisoned by waleed ibn Abdil Malik in Madina

Sayyida Zainab died as a result of poison given by some armies of Yazid in Damascus.

Some Historians said: she died a normal death in Egypt.

The first opinion is what most scholars uphold