"بِسْمِ اللهِ وَلَجْنَا، وَ بِسْمِ اللهِ خَرَجْنَا، وَعَلَى رَبِّنَا تَوَكَّلْنَا".

18. bismillaahi walajnaa, wa bismillaahi kharajnaa, wa 'alaarabblnaa tawakkalnaa

in the name of allah we enter , in the name of allah we leave , and upon our lord we depend [then say as-salaamu '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."