How was Amir al-Mu'minin (PBUH)?

How was He Like?
The martyrdom of Amir al-Muminin (PBUH) is far from our understanding unless we know more about the Imam. And it is such that we cannot even comprehend what it means to lose such a magnanimous person.
Indeed speaking of Amir al-Muminin is a difficult task; his virtues and excellencies are too many to be able to choose. How ironic that his virtues were withheld from being told, (his friends could not express his virtues from fear, and his enemies would not express his virtues from hatred and jealousy), and yet his virtues filled the world.
Hiding the virtues of such a person is not easy and even the worst of his enemies admit this fact.
The following example has been narrated in both Sunni and Shia sources: Zirar ibn Zamrah al-Kinani entered upon Muawiyah. Muawiyah demanded Zirar to speak of Alis (PBUH) character.
Zirar asked to be dismissed from this task. Muawiyah did not allow. Zirar then spoke: Well since I do not have a choice, I will begin. He is far from peoples understanding of people. A strong man; his word was truth and final; he judged fairly; knowledge would erupt from him and insight was obvious within him. He was weary of the world and its benefits, and personal with night and its darkness. By Allah he cried immensely and thought extensively ... He would suffice to the simplest and least in clothing. And instead of soft and delicious food, he would choose to eat rough and hard food without anything to soften it like stew.
By Allah he was like one of us; anytime we would approach him, he would come toward us, and anytime we had a request from him, he would answer us. And even though he was close to us, we wouldnt allow ourselves to speak to him because of the respect he had. His smile was like a pearl, it would organize people of religion, and it would give love to the poor. Men in power did not feel coveted by him in their void acts, and the weak were hopeful to his justice.
By Allah I would see him at times when it was dark, where even a single star could not be seen, he would go toward his prayer altar, he would hold his chin, and cry immensely. I can even hear it now that he would say: O My Lord, O My Lord.
He would supplicate to Allah, and would then tell the world: You have desires for me, you are so fond of me?! Never! Never! Make someone else proud! Trick some other! I distance myself from you every second. I divorce you thrice for your life is too short, and time for you is so invaluable. I cry for the few provisions of my journey, from the far distance of my path, and from its fear.
Muawiyahs tears then began to flow uncontrollably; he dried them with his sleeves, and it was here that those present also began to cry. Muawiyah then said: Yes, this is how Ab al-Hassan was (1)

(Selection taken from the book The First Oppressed Man of the Day by Ayatullah Wahid Khurasani, with minor changes)
References:
1. This incident has been narrated in Shia and Sunni sources. A few of the sources have been mentioned below:
Ahl al-Sunnah Sources: Tarikh Madinah Damishq, vol. 24, p. 401; Heliyat al-Awliya, vol. 1, p. 84; Al-Istiab for Ibn Abd al-Birr, vol. 3, p. 1108
Shiite Sources: Khasais ol Aimmah, p. 70; Manaqib Amir al-Muminin , vol. 2, p. 52; Sharh al-akhbar, vol. 2, p. 391; Kanz al-Fawaid, p. 270; Kashf al-Ghummah, vol. 1, p. 76; Al-Umdah, p. 16..