Allah. This authentic, explicit text makes clear that what al-Hasan did was praiseworthy and pleasing to Allah and His Messenger. It is also established in the Sahīh that:
“The Prophet, may Allah bless him and grant him peace, would seat him on his thigh and also seat Usāmah ibn Zayd, saying: ‘O Allah, I love them both, and I love those who love them.’”
The effects of his love and supplication, may Allah bless him and grant him peace, were also evident in this: both were most eager to achieve that for which the Prophet, may Allah bless him and grant him peace, praised al-Hasan, and most averse to anything contrary to it. This also makes clear that, in the Prophet’s estimation, those killed at Siffīn did not have the same standing as the renegade Khawārij whom he commanded people to fight. Rather, he praised reconciliation between these parties and did not command that they be fought.
For this reason, the Companions and the leading scholars agreed on fighting the renegade Khawārij. ʿAlī, may Allah be pleased with him, openly expressed his joy at fighting them, and his transmission of the Prophet’s command to fight them is well known. As for the fighting among the Companions, no report concerning it was transmitted from the Prophet, may Allah bless him and grant him peace. ʿAlī showed no joy in it; rather, he showed grief, wished that it had not happened, and expressed gratitude to some of the Companions. He also declared both parties free of unbelief and hypocrisy and permitted prayers for mercy upon those killed on either side. These and similar matters establish the agreement of ʿAlī and the other Companions that each of the two parties consisted of believers.
The Quran itself testifies that fighting among believers does not take them outside the faith. Allah Most High says:
“If two groups of believers fight, make peace between them. But if one of them transgresses against