Salallaahu `alayhi wa sallam

From Encyclopedia Islam

The phrase salallaahu `alayhi wa sallam is a phrase Muslims are obligated to say whenever the name of Muhammad (salallaahu `alayhi wa sallam), the Messenger of Allah, is mentioned. It is sometimes translated in English to 'peace be upon him'. Some acronyms are also used, but it is best to either say it outloud when speaking or to write it out when writing.