Written by: Fazilat al-Sheikh Ghulam Mustafa Zaheer Amanpuri Hafizahullah
Sayyiduna Husayn ibn Ali Radi Allahu Anhuma are beloved of Allah, the Messenger of Allah ﷺ, and the Companions of the Messenger Radi Allahu Anhum, therefore love for them is a requirement of faith. Ahl al-Sunnah respect and honor all the Companions and give each Companion their due rights.
Love and respect for Sayyiduna Husayn Radi Allahu Anhu is necessary; insulting him is equivalent to disrespect and inviting the punishment of Allah.
The Late Tabi'i, Abu Rija Atardi Rahimahullah (105 AH) says:
لا تسبوا عليا، ولا أهل هذا البيت، إن جارا لنا من بني الهجيم قدم من الكوفة فقال: ألم تروا هذا الفاسق ابن الفاسق؟ إن الله قتله، يعني الحسين عليه السلام، قال: فرماه الله بكوكبين في عينه، فطمس الله بصره.
Do not speak ill of Sayyiduna Ali Radi Allahu Anhu and his family. A neighbor of ours from Banu Hujaym who came from Kufa said: Look at this sinful son of a sinner, meaning Sayyiduna Husayn عليه السلام, may Allah protect us! Allah destroyed him. Allah placed two heavenly embers in his eyes and his sight was lost.
Reference: (Fada'il al-Sahabah by Ahmad ibn Hanbal: 972, Al-Mu'jam al-Kabir by al-Tabarani: 3/112, Hadith 2830, and its chain is authentic)