Now then, certainly, we and you were on amiable terms as you say but difference arose between us and you the other day, when we accepted belief (īmān) and you rejected it. Today the position is that we are steadfast (in the belief) but you are creating mischief. Those of you who accepted Islam did so reluctantly and that too when all the chief men had accepted Islam and joined the Messenger of Allāh (may Allāh bless him and his descendants).
You have stated that I killed Ṭalḥah and az-Zubayr, forced ‘Ā’ishah out of her house and adopted residence between the two cities (Kūfah and Baṣrah).  These are matters with which you have no concern nor do they involve anything against you. Therefore, no explanation about them is due to you.
You also state that you are coming to me with a party of muhājirūn and anṣār, but hijrah came to an end on the day your brother was taken prisoner. If you are in a hurry, then wait a bit as I may come to meet you and that would be more befitting as that would mean that Allāh has appointed me to punish you. But if you come to me it would be as the poet of Banū Asad said:
They are advancing against summer winds which are hurling stones on them in the highlands and lowlands
(Remember) I have still the sword with which I dispatched your grandfather, your mother’s brother and your brother to one and the same place. By Allāh, I know what you are. Your heart is sheathed and your intelligence is weak. It is better to say that you have ascended to where you view a bad scene which is against you, not in your favour, because you are searching a thing lost by someone else, you are tending someone else’s cattle and you are hankering after a thing which is not yours nor have you any attachment with it. How remote are your words from your actions, and how closely you resemble your paternal and maternal uncles who were led by their wickedness and love for wrong to oppose Muḥammad (may Allāh bless him and his descendants) and in consequence they were killed as you know. They could not put up a defence against the calamity and could not protect their place of safety from the striking of swords which abound in the battle and which do not show weakness.
You have said a lot about killing of `Uthman. You first join what the people have joined (i.e., allegiance) then seek a verdict about (the accused people) from me and I shall settle the matter between you and them according to the Book of Allāh, the Sublime. But what you are aiming at is just the fake nipple given to a child in the first days of stopping of nursing. Peace be on those who deserve it.
 Mu‘āwiyah had written a letter to Amīr al-mu’minīn in which after recalling mutual unity and amicability he laid on him the blame of killing Ṭalḥah and az-Zubayr and ousting ‘Ā’ishah from her house and objected to his adopting Kūfah as his seat of government in place of Medina. In the end, he gave a threat of war and said that he was about to come out with a force of muhājirūn and anṣār to fight. Amīr al-mu’minīn wrote this letter in reply to him, wherein commenting on Mu‘āwiyah’s claim for unity he says that: “There might have been unity between you and us but with the advent of Islam such a gulf has developed between the two that it is not possible to bridge it, and such a separation has occurred which cannot be removed. This was because we responded to the call of the Prophet and hastened towards Islam but your position was that you were still in the state of unbelief and ignorance whereby we and you came to adopt separate ways. But when Islam secured stability and the chiefs of Arabs entered its fold you too were obliged to, and secured protection of your lives by putting the covering of Islam on your faces, but continued secretly to fan the mischief intended to shatter its foundations. Since we had accepted Islam of our own free will and pleasure we adhered to the right path and at no stage did any faltering occur in our steadfastness. Therefore, your acceptance of Islam too could not make us agree with your views.”
As regards Mu‘āwiyah’s accusation that Amīr al-mu’minīn engineered the killing of Ṭalḥah and az-Zubayr; then even if this blame is admitted as true, is it not a fact that they had openly revolted against Amīr al-mu’minīn and had risen for war after breaking the allegiance. Therefore, if they were killed in connection with the revolt their blood would be wasted and no blame would lie on the killer, because the penalty for him who revolts against the rightful Imām is death, and fighting against him is permissible, without doubt. The fact however, is that this accusation has no reality because Ṭalḥah was killed by a man of his own party. Thus, the historians write :
Marwān ibn al-Ḥakam shot Ṭalḥah with an arrow and turning to Abān ibn ‘Uthmān said: “We have killed a killer of your father and relieved you of revenge.” (Ibn Sa‘d, vol. 3, part 1, p. 159; Ibn al-Athīr, vol. 3, p. 244; al-Istī‘āb, vol. 2, pp. 766 -769; Usd al-ghābah, vol. 3, pp. 60, 61; al-Iṣābah, vol. 2, p. 230; Tahdhīb, at-tahdhīb, vol.5, p.21).
As for az-Zubayr, he was killed by ‘Amr ibn Jurmūz on his way back from Baṣrah, and there was no prompting by Amīr al-mu’minīn in it. Similarly, ‘Ā’ishah herself came out of her house as the head of this rebellious group while Amīr al-mu’minīn counselled her several times to realize her position and not to step out of her bounds but these things had no effect on her.
Of the same type was his criticism that Amīr al-mu’minīn left Medina and adopted Kūfah as the seat of his government because Medina turns out bad people from itself and throws away dirt. The reply to it is only this that Mu‘āwiyah himself too always retained Syria as his capital keeping away from Medina.
In this way, what right can he have to object to Amīr al-mu’minīn changing his seat. Amīr al-mu’minīn left Medina because of those rebellions which had cropped up from all sides. To suppress them only the selection of such a place as capital from where military assistance could be mobilized at any time could be useful. Thus, Amīr al-mu’minīn had seen on the occasion of the battle of Jamal that a great majority of the people of Kūfah had supported him and that therefore by making it a base for the army, defence against the enemy could be easily managed, while Medina was not appropriate for military mobilization or for supplies.
Lastly, as for Mu‘āwiyah’s threat that he would march with muhājirūn
and anṣār, Amīr al-mu’minīn gave a reply to this point in a very subtle way, namely that, “How would you bring muhājirūn now since the door for hijrah was closed the day when your brother Yazīd ibn Abī Sufyān was taken prisoner.” This man was taken prisoner on the day of the fall of Mecca and there is no question of hijrah after the fall of Mecca so as to enable anyone to be called a muhājir because of the Prophet’s saying: “There is no hijrah after the victory over Mecca.”