Bismillāhi walajnā,
wa bismillāhi kharajnā,
wa `ala Rabbinā tawakkalnā
In the Name of Allah we enter ,
in the Name of Allah we leave ,
and upon our Lord we depend
[then say As-Salāmu `Alaykum to those present].
Reference:
Abu Dawud 4/325. Muslim {Hadith no. 2018) says that one should mention the
Name of Allah when entering the home and when beginning to eat; and that
the devil, hearing this, says: "There is no shelter for us here tonight and
no food."
