He said: Abul Hasan Ali b. Muhammad b. Hubaysh al-katib reported to me from al-Hasan b. Ali al-Za'farani, who reported from Ibrahim b. Muhammad al-Thaqafi, from Muhammad b. Zakariyya, from Abdullah b. al-Dhahhak, from Hisham b. Muhammad, who said:
When news of the assassination of Muhammad b. Abi Bakr, may Allah be pleased with him, reached Amirul Momineen, peace be upon him, he wrote to Malik b. al-Harith al-Ashtar, may Allah bless him with mercy, who was then residing at Nasibayn. (He wrote): "You are surely among those from whom I seek help to keep the banner of Islam high and to crush the haughtiness of the disobedient and to fortify the threatened borderline. I had appointed Muhammad b. Abi Bakr, may Allah bless him with mercy, to govern Egypt, but the rebels attacked him and as he was inexperienced about warfare, he was martyred - may Allah bless him with mercy. Now, come over to me so that we may look into the matter concerning Egypt, and appoint in your place a reliable, sane person from your companions." Then Malik - may Allah be pleased with him, appointed Shabib b. Amir al-Azadi to succeed him, and proceeded till he arrived to meet Amirul Momineen, peace be upon him. Then he (i.e. Ali) explained to him the situation in Egypt and informed him about its people.

Then he said: "There is no one for this assignment except you, so be ready to go. And if there is anything, about which I have not guided you, you will depend upon your judgement and seek assistance from Allah for your intention. (In your dealing with them), mix severity and harshness with tenderness and gentleness, and be friendly for as long as friendliness serves the purpose. And be resolute when there is no alternative to severity."
He said: Then Malik al-Ashtar - may Allah be pleased with him, rose and prepared for his journey to Egypt. And Ali, peace be upon him, sent a letter to the people of Egypt, before (Malik) arrived there:
"In the name of Allah, Most Merciful, Most Benevolent, I praise Allah, none to be worshipped but He; and beseech Allah to bless His Prophet, Muhammad and his progeny. Surely, I have sent unto you a servant from the servants of Allah, who does not sleep in the days of fear and does not recoil from the enemy fearing any disaster. He is from the strongest among His servants and the noblest; and to the transgressors, more threatening than the burning fire. And from ignorance and blemish, he is the farthest. He is Malik b. al-Harith al-Ashtar, neither a cutting tooth nor a blunted edge. He is patient amid threats, calm and composed at the time of war. He has an original judgement and an agreeable patience. So listen to him and obey him. If he commands you to march forth, march, and if commands you to halt, halt. For he does not advance or halt except by my order. I have sent him to you in spite of my need for him, for the sake of your welfare and because of my deep concern about your adversaries. May Allah guard and protect you with guidance and keep you steadfast with Taqwa. May He bless us and you with what He likes and loves. May peace and mercy of Allah and His Blessing be upon you."
When Malik al-Ashtar completed his preparations for journey to Egypt, the spies of Mo'awiyah from Iraq wrote to inform him. He was very much distressed, because he had his eyes set on Egypt. He knew that he would lose Egypt if al-Ashtar arrived there and to him al-Ashtar was a more powerful person than the son of Abu Bakr. So he contacted a chief who paid the revenue at a place called al-Qulzum, informing him that Ali (AS) has appointed al-Ashtar to govern Egypt and if you got rid of him on my behalf, I shall gift away the revenue to you for as long as you live. So plan to kill him in every way possible. Then Mo'awiyah collected the people of Syria and said: "Verily, Ali has sent al-Ashtar to Egypt. Come and let us pray to Allah that He may relieve us of him." Then he prayed, and so did the people with him.

Al-Ashtar travelled on till he came to al-Qulzum. The chief received him and greeted him and then said: "I am among those who is liable to pay the revenue. And you and your companions have a right upon all that grows on my land. So be my guest and allow me to serve you and your companions and let your animals freely graze on my land, and I will count it from my liability."
So, al-Ashtar became his guest and he served him (al-Ashtar) and his companions for all their needs. And he brought to them food, including some honey, which had poison. When al-Ashtar drank from that honey, it killed him and he died because of that.
Mo'awiyah got the news, so he collected the people of Syria and said: "Happy tidings for you! Allah, Most High, has answered your prayers; has relieved you of him and has killed him." They rejoiced.
And when the news of Ashtar's death assailed Amirul Mo'mineen, peace be upon him, he sighed and grieved, saying: "What an excellent man Malik was! Had he been a mountain, he would have been its firm rock, and had he been from stone, he would have been solid. By Allah, some men in the world will be placated by his death; but it behaves for the mourners to mourn over him." Then he said: "We are for Allah and unto Him shall we return; and all praise to Allah, the Lord of all Universe. I shall seek reward from You for this sacrifice, for surely, his death is among the greatest worldly calamities. May Allah bless Malik with mercy; no doubt, he faithfully dispersed his charge and completed the appointed term (of life) and met his Creator; while we have reconciled ourselves to forbear every adversity after being bereaved of the Prophet, peace be upon him and his progeny, for that was the greatest calamity
Source:
Al-Amali: The Dictations of Sheikh al-Mufid