Praise be to Allaah.

Shaykh al-Islam Ibn Taymiyah was asked about a man who said that ‘Ali ibn Abi Taalib was not one of the Ahl al-Bayt (members of the Prophet’s household) and that it is not permissible to send blessings upon him, and that sending blessings upon him was bid’ah (an innovation). 

He replied: 

With regard to ‘Ali ibn Abi Taalib being one of the Ahl al-Bayt, this is something concerning which there is no difference of opinion among the Muslims. It is so obvious to the Muslims that there is no need for evidence to prove it. Rather he is the best of the Ahl al-Bayt, the best of Bani Haashim after the Prophet (peace and blessings of Allaah be upon him). It was proven that the Prophet (peace and blessings of Allaah be upon him) threw his cloak over ‘Ali, Faatimah, Hasan and Husayn and said, “O Allaah, these are the members of my household, so to remove Ar-Rijs (evil deeds and sins) from them and purify them with a thorough purification [cf. al-Ahzaab 33:33].” 

With regard to sending blessings exclusively upon him, this issue leads us to another issue, which is whether it is permissible to send blessings exclusively upon anyone other than the Prophet (peace and blessings of Allaah be upon him), such as saying, “O Allaah send blessings on ‘Umar, or ‘Ali (Allaahumma salli ‘ala ‘Umar etc.)”. The scholars disputed concerning that. Maalik, al-Shaafa’i and a group of the Hanbalis said that we should not send blessings exclusively upon anyone except the Prophet (peace and blessings of Allaah be upon him), as it was narrated that Ibn ‘Abbaas said: “I do not know that blessings should be sent upon anyone except the Prophet (peace and blessings of Allaah be upon him). Imaam Ahmad and most of his companions said that there was nothing wrong with that, because ‘Ali ibn Abi Taalib said to ‘Umar ibn al-Khattaab, “May Allaah send blessings upon you.” This is the more correct view. But singling out one of the Sahaabah or relatives of the Prophet (peace and blessings of Allaah be upon him), such as ‘Ali, or anyone else, to send blessings upon them, is a form of making them rival the Prophet (peace and blessings of Allaah be upon him), in such a way that this phrase becomes like a symbol or slogan that is attached to his name, this is what is bid’ah.