Is the aforementioned Hadith about the killing of the People of the House (Ahl al-Bayt) an authentic Hadith?

The aforementioned hadith was narrated by Ibn Majah, Al-Hakim in his Mustadrak, Al-Bazzar, Al-Tabarani, and Ibn Abi Shaybah, and it is weak or fabricated. However, the part about the Mahdi in it is authentic through many other chains of transmission. Many scholars have affirmed the authenticity of the hadiths concerning the Mahdi, among them Shaykh al-Islam Ibn Taymiyyah and his student Ibn al-Qayyim. Scholars have explicitly stated that the hadiths about the Mahdi are mutawatir ma'nan (concurrent in meaning).