Question:

Many people write the salutation to the Prophet with (Saad) or with (Saad, Laam, Ain and Meem) as an abridgement. What is the ruling on this?

Answer:

Some of the scholars have cautioned against this. It is not befitting, and it is falling short in fulfilling the rights of the Prophet, as pointed out by a group of those amongst the scholars—those who author (books) on the subject matter of the science of hadeeth. It is not befitting to limit the (salutation to the Prophet in writing) with Saad, Laam, Aim or with Saad alone; rather it should be written completely [i.e. صلى الله عليه وسلم ]

Al-Markaz As-Salafi

[Source:Al-Fataawaa Wad-Duroos Fil Masjid Al-Haraam of Shaikh Abdullaah Bin Muhammad Bin Humaid: page:140-141]