ومن كتاب له (عليه السلام) إلى أبي موسى الأشعري وهو عامله على الكوفة، وقد بلغه عنه تثبيطه الناس عن الخروج إليه لما ندبهم لحرب أصحاب الجمل
To Abū Mūsā (‘Abdullāh ibn Qays) al-Ash‘arī, the Governor of Kūfah when Amīr al-mu’minīn learned that he was dissuading the people of Kūfah from joining in the battle of Jamal when Amīr al-mu’minīn had called them to fight along with him.
Now, I have come to know of words uttered by you which go in your favour as well as against you.  So, when my messenger reaches you prepare yourself and get ready, come out of your den and call those who are with you. Then, if you are convinced of the truth get up but if you feel cowardice go away. By Allāh, you will be caught wherever you may be and you will not be spared till you are completely upset and everything about you is scattered and till you are shaken from your seat. Then, you will fear from your front as you do from the rear.
What you hope is not a light matter, but it is serious calamity. We have to ride its camels, overcome its difficulties and level its mountains. Set your mind in order, take a grip on your affairs and acquire your (lot and your) share. If you do not like it then go away to where neither you are welcome nor can you escape from it. It is better that you be left alone and lie sleeping. Then no one will enquire where so-and-so is. By Allāh, this is the case of right with the rightful person and we do not care what the heretics do; and that is an end to the matter.
 When Amīr al-mu’minīn had the idea of suppressing the revolt of the people of Baṣrah he sent this letter through Imām al-Ḥasan to Abū Mūsā (‘Abdullāh ibn Qays) al-Ash‘arī, who had been appointed Governor of Kūfah by ‘Uthmān, wherein he has ascolded him for his duplicit and contradictory behaviour and attempted to persuade him to jihād, because on one side he used to say that Amīr al-mu’minīn was the true Imām and allegiance to him was right and on the other he said that to support him in fighting against the Muslims was not right; but it was a mischief and it was necessary to keep off this mischief. Thus, Amīr al-mu’minīn has referred to this contradictory view by the words “huwa laka wa ‘alayka” (which go in your favour as well as against you). The intention is that when Amīr al-mu’minīn is the rightful Imām how can fighting his enemy with him be wrong? And if fighting on his side is wrong then what is the meaning of his being the rightful Imām.
In any case, in spite of his dissuading from fighting, the people of Kūfah came out in large numbers to join Amīr al-mu’minīn’s army and took full part in the battle, giving such a defeat to the people of Baṣrah that they never again dared to revolt.