In a rigorously authenticated (sahih) hadith. Abu Hurayra |RadiAllaho unho| relates,
The messenger of Allah |Sal lal laho alaihe wasl'lam said 'O people! indeed Allah is pure; He does not accept anything but what is pure. And Allah has commanded of the believers what he has commanded of the messengers. He says, "O messengers, eat of what is wholesome and do righteous deeds. Indeed, I am all-knowing of what you do" (Qur'an 23:51). And he says, "O you who belive, eat of the wholesome things that We have provided you" (Qur'an :172). He then related the story of a person who has traveled a long way [for some righteous purpose], and whose clothes have becomme tattered and dirtied. He extends his hands to the heavens, sayin, ' O my Lord! O my Lord!' But what he has eatin is unlawful (haram), and what he has drunk is unlawful, and what he wears is unlawful, and he has been nourished with what is unlawful -- So how can he be answered?" (Sahih Muslim)By putting in the any food or drink that Allah, the Creator of the Worlds, has deemed unlawful and impure, our bodies become reservoirs for impurity. Just as a Muslim's prayer is unacceptable if he or she is in a state of outward physical impurity, how can our prayers or our supplications or any of our other acts of worship deserve to be accepted if we offer them while impurity runs through the veins of our bodies?
Therefore, from both a practical and, more importantly, from a textual perspective, there is no question that we as Muslims have a solemn religious duty to learn the laws of Islam regarding lawful food and drink and make every effort to adhere to them.
(The Islamic Laws of Animal Slaughter - Mufti Muhammad Taqi Usmani pg 11-12)