(بِسْمِ اللَّهِ وَلَجْنَا، وَبِسْمِ اللَّهِ خَرَجْنَا، وَعَلَى اللَّهِ رَبِّنَا تَوَكَّلْنَا، ثُمَّ لِيُسَلِّمْ عَلَى أَهْلِهِ).
In the name of Allah we enter and in the name of Allah we leave, and upon our Lord we place our trust. [then say As-Salāmu `Alaykum to those present].
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."