Gelatine and Investigating Ingredients
Taken from sistani.org
Question: Gelatin is used in a number of drinks and food items in the West. We do not know that gelatin has been extracted from a vegetable or an animal source; and that if it is from an animal, is it from its bones or from the tissues around the bones; neither do we know if the animal was one that is halal for us or haram. Are we allowed to eat such gelatin?
Answer: It is permissible to eat if the doubt is whether it has been extracted from an animal or vegetable. But, if it is known that it was derived from an animal, then it is not permissible to eat without ascertaining that the animal was slaughtered according to shari‘a. This prohibition applies, as a matter of obligatory precaution, even if it was extracted from animal bones.
Of course, if a chemical change occurs in the original ingredients during the process of manufacturing the gelatin, there is no problem at all in eating it. Similarly, even if one has doubt whether the animal was slaughtered Islamically or not, still there is no problem in adding the gelatin [made from that animal] to the food in such a minute amont that it is completely absorbed in it (Sistani.org)
Question: We are unaware of the ingredients of food sold in shops in Western countries: it might be free from those ingredients that are forbidden to us or it might contain them. Are we allowed to eat such items without looking into their ingredients, or inquiring about them? Or is that not allowed to us?
Answer: It is permissible [to eat such food] as long as it is not known that it contains meat, fat, and their derivatives that are forbidden to us. (Sistani.org)
All kinds of packed food with the exception of meat, fat and their extracts, are permissible for a Muslim, even if he doubts that its ingredients might contain what is forbidden for him or even if he doubts that the cook —whosoever he may be— had touched it with wetness. It is not obligatory on him to inquire about its ingredients to ensure that it does not contain anything that is forbidden to him.
In short, all kinds of food with the exception of meat, fat, and their extracts are permissible for a Muslim, even if he doubts that it might contain something which is forbidden for him to eat or doubts that its cook—whosoever he may be—had touched it with wetness. (Sistani.org)
Just as it is not obligatory on him to inquire about the ingredients of such food to ensure that it is free from what is forbidden to him, it is not obligatory on him to ask the cook whether he touched it while preparing the food or after it. (Sistani.org)
Assume a land animal is not permissible (halal) unless [i.e. a land animal is halal if] (1) it is known to be muhallal [halal animal to eat after proper slaughter] and mudhakkah [properly slaughtered]; (2) it is procured from a Muslim; (3) it is procured from a Muslim market; or (4) it is procured from a Muslim land. (IMAM-US) (Brackets mine)
Ali ibn Ibrahim has narrated from his father from ibn abu ‘Umayr from ‘Umar ibn ‘Udhaynah from al-Fudayl, Zurarah, and Muhammad ibn Muslim who have said the following: “They had asked abu Ja‘far, ‘Alayhi al-Salam, about the meat from the market place about which one does not know what the butchers do. He (the Imam), ‘Alayhi al-Salam, said, ‘You can use it for food if it is in the market place of Muslims and do not ask about it.’” (Al Kafi)
The Sunnah that one should not heed their doubts
[2/93] al-Faqih and al-Tahdhib: From Ibn Mahbub from Abdallah b. Sinan who said: Abu Abdillah عليه السلام said: everything which has both Halal and Haram [elements mixed into it] then it is Halal for you forever until you know the Haram in it specifically so you abandon it. (Mu'jam al Hadith al Mu'tabara)
Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from ibn Mahbub from ‘Abdallah ibn Sinan who has said the following. “I mentioned a person, who would overdo the deeds of his doing Wudu and prayer to Imam abu ‘Abdallah (a.s) and added that he is a man of good intelligence.” The Imam (a.s) then said, ‘What kind of intelligence is it that allows him to obey Satan.’ I then asked the Imam, “How would he be considered as obeying Satan?” The Imam (a.s) said, “Ask him wherefrom this thing comes to him. He will certainly say, “It comes from Satan.” (Al Kafi)
[I say: this hadith shows that acting on one's doubt where one should not act on it is an act of obeying Satan. And indeed, investigating where it is not obligated is against the Sunnah.]