Ruling on using phrase 'peace be upon him' to anyone other than the Messenger
While reviewing the topics in the book “‘Aqd Al-Durar fi Akhbar Al-Muntadhar”, I found some narrations reported on the authority of ‘Ali ibn Abu Talib as follows: On the authority of ‘Ali ibn Abu Talib (peace be upon him) who narrated that the Messenger of Allah (peace be upon him) said: “One of my family will come out in nine banners. (i.e. detachments).” What is the ruling on saying “peace be upon him” and the like phrases when referring to people other than the Messenger (peace be upon him)?
It is not permissible to single out ‘Ali (may Allah be pleased with him) with this phrase. Rather, it is permissible to say when referring to him and to other Sahabah (Companions of the Prophet) “may Allah be pleased with them” or “may Allah be merciful with them” because there is no evidence on singling him out with this phrase to the exclusion of other Sahabah. Likewise, there is no evidence on singling him out with the phrase “may Allah honor his face”.
It is better to treat him in the same way of treating other Rightly-Guided Caliphs and not to single him out with certain phrases which have no evidence supporting them.