Advice of Scholars - SAYING THE BISMILLÂH
It is written on the sixth page of the first volume of Ibni Âbidîn, “It is wâjib to say Bismillâh or Allâhu akbar when killing an animal (by cutting its throat), when shooting an arrow at a game animal, when sending a trained hound for the animal to be hunted. It is acceptable as well to say the Basmala completely. There are those who say that it is wâjib to say the Basmala before reciting the Fâtiha at each rak’at. Yet, more correctly, it is sunnat. It is sunnat to say the Basmala when beginning to perform an ablution, to eat, to drink and to do any useful work. It is either permissible or mustahab to say the Basmala between the Fâtiha and the sûra (which is to be recited after the Fâtiha while performing namâz). It is mubâh to say it when beginning to walk, when sitting down or standing up.
“It is makrûh to say the Basmala when opening one’s private parts, when entering a place where there is najâsat, when reciting Barâa Sûra immediately after the sûra previous to it, when beginning to smoke a cigarette or to eat something with a strong smell, such as onions or garlics, [and when beginning to shave. The fact that the cigarette is compared to things with a strong smell, such as onions and garlics, shows that tobacco is, like these things, tab’an makrûh, not shar’an makrûh. ] It is harâm to say the Basmala when beginning to commit a harâm. In fact, it has been said that he who says the Basmala knowingly when beginning something which is certainly harâm becomes a disbeliever. It is harâm for a (person who is in the state of) junub to recite the Qur’ân with the intention of reciting the Qur’ân.
“It is wâjib to say hamd in namâz, and it is sunnat to say it in a khutba or before each du’â (prayer) or after eating and drinking. It is mubâh to say it whenever you remember it. It is makrûh to say it at dirty places, and it is harâm to say it after eating or drinking something which is harâm; it may even cause disbelief.”