Al-Hafiz Ibn Kathir the Damascene on the extremist Rafidi cult:

ولكنهم (الرافضة) طائفة مخذولة وفرقة مرذولة يتمسكون بالمتشابه، ويتركون الأمور المحكمة المقدرة عند أئمة الإسلام – البداية والنهاية – ابن كثير – ج ٥ – الصفحة ٣٠٨ 

“But they (the Rafidah) are a forsaken sect and a disgraced faction; they cling to the ambiguous and abandon the decisive matters determined by the Imams (scholars) of Islam.” (Al-Bidayah wa Al-Nihayah by Ibn Kathir, vol. 5, pg. 308)

Ibn Kathir on the tragedy of Karbala:

“Every Muslim should feel saddened by his (i.e. sayyiduna Al-Husayn’s) killing, may Allah be pleased with him, as he was among the leaders of the Muslims and a knowledgeable companion. He was the son of the daughter (i.e. sayyidah Fatimah) of the Messenger of Allah, peace and blessings be upon him, who is the best of his daughters. He was a devout, brave, and generous person. However, there is nothing good in what the Shia [Rafidah] do in expressing excessive distress and grief, most of which may be done in order to show off.

Even his father, who was better than him, was killed, yet they (the Shia) do not mourn his death like they do on the day of Al-Husayn’s killing. His father was killed on a Friday while going to the Fajr prayer on the 17th of Ramadan in the year 40 AH. Similarly, Uthman, who was better than Ali according to Ahl al-Sunnah wa al-Jama’ah, was killed while being confined in his house during the days of Tashriq in the month of Dhu al-Hijjah, year 36 AH. He was killed in a brutal manner, yet people did not make the day of his death a day of mourning.

Likewise, Umar ibn al-Khattab, who was better than both Uthman and Ali, was killed while leading the Fajr prayer in the mosque, reciting the Quran. People did not make the day of his death a day of mourning either. Abu Bakr, who was better than all of them, also passed away, and people did not make the day of his death a day of mourning. The Messenger of Allah, peace and blessings be upon him, is the leader of the children of Adam in this world and the Hereafter, and Allah took him to Himself just as He took the prophets before him. However, no one made the day of their deaths a day of mourning, nor did anyone mention [reliable evidence for] any of the things that these ignorant Rafidis claim happened on the day of Al-Husayn’s death, such as solar eclipses, the appearance of redness in the sky, and other such matters.

“And the best thing to be said when mentioning these calamities and the like is what Ali ibn al-Husayn narrated from his grandfather, the Messenger of Allah, peace and blessings be upon him, that he said: ‘Whenever a Muslim is afflicted with a calamity, and he remembers it and bears it patiently, even though it may have happened a long time ago, he will be rewarded by Allah with the same reward as if it happened on the day it occurred.'” (Al-Bidayah wa Al-Nihayah by Ibn Kathir, vol. 8, pg. 221)