Peace be upon him is a phrase that Muslims often say after saying (or hearing) the name of a prophet of Islam. There are two variants of this phrase in Arabic:
In Arabic these salutations are called salawat. 'Peace be upon him' is abbreviated to SAW (in accordance with the Arabic words sallallahou alayhi wasallam) or PBUH (according to English).
The phrase is also encoded as a ligature at Unicode codepoint U+FDFA SALLALLAHOU ALAYHI WASALLAM.
In the translation of the meanings of the Qur'an in Surah 33 entitled Al-Ahzab (The Confederates), ayah (verse) 56:
The Islamic scholar, ibn Kathir, entitled the section in his tafsir (i.e., explanation of the Qur'an) regarding this verse, "The Command to say Salah upon the Prophet (Muhammad)."
This point is further founded in the saying by Muhammad that, "The misser is the one in whose presence I am mentioned, then he does not send the Salah upon me." This was recorded by Ahmad ibn Hanbal in his Musnad.
At-Tirmidhi recorded that Abu Hurayrah said:
At-Tirmidhi said that this hadith was, "Hasan gharib" (Good but only reported once).
Sahih Muslim, Sunan Abu Dawud, Sunan at-Tirmidhi, and Sunan an-Nasa'i, recorded that Abu Hurayrah said,
Imam Ahmad ibn Hanbal reported in his Musnad that the companion of Muhammad, Abu Talhah al-Ansari said:
The isnad (chain of narrators) of this hadith is good.
It was reported by Razin ibn Mu'awiyah in his book Jami al-Usool that Muhammad said:
"As it is prescribed to send blessings upon the Prophet (peace and blessings of Allah be upon him) in prayer when saying the tashahhud, and it is prescribed when giving khutbahs, saying Du’a and praying for forgiveness, and after the Adhan, and when entering and exiting the mosque, and when mentioning him in other circumstances, so it is more important to do so when writing his name in a book, letter, article and so on. So it is prescribed to write the blessing in full so as to fulfil the command that Allah has given to Muslims, and so that the reader will remember to say the blessing when he reads it. So one should not write the blessing on the Prophet (peace and blessings of Allah be upon him) in short form such as writing (S) or (SAWS) etc, or other forms that some writers use, because that is going against the command of Allah in His Book, where He says (interpretation of the meaning):
And that (writing it in abbreviated form) does not serve that purpose and is devoid of the virtue of writing 'salla Allaahu ‘alayhi wa salaam (May Allah send blessings and peace upon him)' in full. Moreover the reader may not take notice of it and may not understand what is meant by it. It should also be noted that the symbol used for it is regarded as disapproved by the scholars, who warned against it."
When mentioning sahaba (the companions of Muhammad), radhi Allahu anhu (for males) and radhi Allahu anha (for females) are used by Sunnis; they mean may Allah be pleased with him or her respectively. The phrase is sometimes also used after mentioning other names including that of Jesus and Moses, but the term عليه سلام aleyhi salaam, "On him be peace" is more common. See for example letter from Mahmoud Ahmadinejad, President of Iran, to G. W. Bush: "Can one be a follower of Jesus Christ (PBUH), the great Messenger of God, Feel obliged to respect human rights ..."