The virtue of ‘Ali ibn Abi Taalib and the ruling on sending blessings exclusively upon him

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.