When slaughtering, I said “Bismillâh al-Rahmân al-Rahîm” instead of “Bismillâh wa Allah Akbar”. Was the meat of that slaughtered animal lawful or unlawful? what should one do in this case?
You may say “Bismillâh” (In the namer of Allah) or “Bismillâh wa Allah Akbar” (In the name of Allah; Allah is the greatest). It is permissible to add: “Rabbanâ taqabbal minnâ” (Our Lord, accept this from us).
Since you can suffice with “Bismillah”, then the slaughtering will still be correct if you add “al-Rahmân al-Rahîm” (the Beneficent, the Merciful). However, it is preferrable not to say something that is not established by the Sunnah.
Source: Islam Today
-- Al Arabiya Digital