In the 40th year of Hijri, in the early hours of the morning of 19th Ramadan, Imam Ali (AS) was struck with a poisoned sword by the Kharijite Ibn Muljim (may the curse of Allah be upon him) while leading prayers in the Masjid of Kufa.

He was martyred on the 21st day of Ramadan 40 A.H. and buried in Najaf-ul-Ashraf. He was born in the House of Allah, the Ka'ba, and martyred in the House of Allah, Masjid-e-Kufa. The Lion of Allah, the most brave and gentle Muslim after the Holy Prophet (S) himself, began his glorious life with devotion to Allah and His Messenger, and ended it in the service of Islam.

"And do not speak of those who are slain in the Way of Allah as dead; nay, they are alive, but you perceive not." Qur'an 2:154

Ameer-ul Momineen Al-Imam Ali ibn Abi Talib (AS) last will to his sons Imam Hasan (AS) and Imam Hussain (AS) following a fatal blow on his head during morning prayers by Ibn Muljim (A Kharijite):

My advice to you is to be conscious of Allah and steadfast in your religion. Do not yearn for the world, and do not be seduced by it. Do not resent anything you have missed in it. Proclaim the truth; work for the next world. Oppose the oppressor and support the oppressed.

I advise you, and all my children, my relatives, and whosoever receives this message, to be conscious of Allah, to remove your differences, and to strengthen your ties. I heard your grandfather, peace be upon him, say: "Reconciliation of your differences is more worthy than all prayers and all fasting."

Fear Allah in matters concerning orphans. Attend to their nutrition and do not forget their interests in the middle of yours.

Fear Allah in your relations with your neighbors. Your Prophet often recommended them to you, so much so that we thought he would give them a share in inheritance.

Remain attached to the Quran. Nobody should surpass you in being intent on it, or more sincere in implementing it.

Fear Allah in relation to your prayers. It is the pillar of your religion.

Fear Allah in relation to His House; do not abandon it as long as you live. If you should do that you would abandon your dignity.

Persist in jihad in the cause of Allah, with your money, your souls, and your tongue.

Maintain communication and exchange of opinion among yourselves. Beware of disunity and enmity. Do not desist from promoting good deeds and cautioning against bad ones. Should you do that, the worst among you would be your leaders, and you will call upon Allah without response.

O Children of Abdul Muttalib! Do not shed the blood of Muslims under the banner: The Imam has been assassinated! Only the assassin should be condemned to death.

If I die of this stroke of his, kill him with one similar stroke. Do not mutilate him! I have heard the Prophet, peace be upon him, say: "Mutilate not even a rabid dog."

Source: Nahjul Balaghahah (Peak of Eloquence)