Is it permissible to use the phrase "peace be upon him/her/them" (عليه السلام) for each of Ali ibn Abi Talib, Fatimah al-Zahra, Al-Hasan, and Al-Husayn?

Scholars differ on invoking blessings and peace upon individuals other than prophets in isolation. The majority of scholars dislike this, as the Salaf (early Muslims) did not use it except for the prophets. Moreover, it has become a شعار (distinctive mark or slogan) for people of innovation (Ahl al-Bid'ah) when referring to some Companions but not others, and we have been prohibited from resembling them.

Al-Nawawi said: "Blessings are not invoked upon anyone other than prophets except as a follow-up, because the invocation of blessings (Salah) is specific to them in the language of the Salaf, just as 'Azza wa Jall' (Mighty and Exalted) is specific to Allah. So, one does not say 'Abu Bakr, may Allah bless him and grant him peace' (salla Allahu alayhi wa sallam), even if the meaning is sound. The most authentic and well-known view is that singling out individuals other than prophets for blessings is disliked, a disliking of tanzih (discouragement rather than prohibition), because it is a شعار for people of innovation."

It is permissible for individuals other than prophets to be included as a follow-up, such as "O Allah, bless Muhammad and the family of Muhammad," because the Salaf did not prohibit this, and we are commanded to do so in the Tashahhud.

As for peace (Salam), it is not invoked singularly upon individuals other than prophets when referring to them in their absence, such as saying "Ali, upon him be peace." However, it is permissible to address the living and the dead with it, such as "Peace be upon you" (Assalamu alaykum).

Ibn Kathir is of the view that singling out Ali with "upon him be peace" or "may Allah honor his face" without the rest of the Companions, even though its meaning is sound, is for the purpose of veneration. However, there should be equality among the Companions in this regard.

In conclusion, neither Ali, nor Fatimah, nor Al-Hasan, nor Al-Husayn should be singled out for blessings or peace individually. Rather, they and all other Companions are equal, with the disliking of using this phrase for anyone other than the prophets.