Hz. Ali RA was murdered while he was in the state of prayer, his youngest son Hussein RA died as a martyr in battle while fighting with around 100 men against an army set up by the Ummayad caliphate, Hussein's infant son was killed during that battle as well, Shias commemorate his death with a protest of mourning each year during muharram. He is considered the martyr of martyrs. He sacrificed everything for righteousness.
Imam Hussein(as) says Oh Allah, I have left the entire world for the sake of You, And I have orphaned my children so that I be with You. So if I am cut into pieces for the love of You, my heart would lean to none other than You.