BISMILLAH بسم الله
Lit. “In the name of God.” An ejaculation frequently used at the commencement of any undertaking. There are two forms of the Bismillah: –
1. Bi-’smi ‘llahi ‘r-rahim, i.e. “In the name of God, the Compassionate. the Merciful.” This is used at the commencement of meals, putting ou new clothes, beginning any new work, and at the commencement of books. It occurs at the head of every chapter or surah in the Qur’an, with the exception of the ixth (i.e. the Suratu ‘l-Bara’ ah).
2. Bi-’smi ‘llahi ‘llahi ‘l-akbar, i.e. “In the name of God. God the Most Great.” Used at the time of slaughtering of animals, at the commencement of a battle, &C, the attribute of mercy being omitted on such occasions.
The formula Bi-’smi ‘llahi ‘r-rahmani ‘r-rahim is of Jewish origin. It was in the first instance taught to the Quraish by Umaiyah of Ta’if, the poet, who was a contemporary but somewhat older than, Muhammad, and who, during his mercantile journeys into Arabia Petraea and Syria, had made himself acquainted with the sacred books and doctrines of Jews and Christians. (Kitaba’l -Aghani, 16, Delhi; quoted by Rodwell.)
Based on Hughes, Dictionary of Islam