إِنَّ اللَّهَ وَمَلَائِكَتَهُ يُصَلُّونَ عَلَى النَّبِيِّ ۚ يَا أَيُّهَا الَّذِينَ آمَنُوا صَلُّوا عَلَيْهِ وَسَلِّمُوا تَسْلِيمًا
Indeed, Allah confers blessing upon the Prophet, and His angels [ask Him to do so]. O you who have believed, ask [ Allah to confer] blessing upon him and ask [ Allah to grant him] peace.
As is well-established by the primary sources, Muslims regularly send their blessings on the prophet Muhammad; this is often done by mentioning the salawat after any mention of his name. In Arabic, the construction
صلى الله عليه وسلم is the most common, which translates to
May God's blessings and peace be upon him.
In English, however, this is often translated as
Peace be upon him, which only accounts for half (and arguably the less-important half) of the salat. "Peace be upon him" is more accurately a translation of
عليه السلام which, while also a common salat, is rarely (if ever) used among Arabic-speaking Muslims for the prophet Muhammad himself.
In English, the
Peace be upon him construction is predominant where an Arabic-speaking Muslim would use
صلى الله عليه وسلم, that is to say it is reserved for the prophet Muhammad himself. To a lesser extent, it is also used for other prophets or notable figures as the Arabic
عليه السلام would be.
Given that the Arabic text is hardly ambiguous in this regard, and the very term salat is derived from the root
ص ل و (meaning prayer, or blessing), it would seem that the most important part to translate would be the
صلى الله (God's blessings). To me, it seems an odd sort of mistake for any Islamic scholar worth his salt to make. This suggests that either there's a wisdom behind this translation that I don't understand, or it was translated thus through distinctly non-Islamic channels (at which point, the universality of the phrase among English-speaking Muslims seems peculiar).
So where did this translation come from, and why is it so prevalent among English-speaking Muslims today?