Praise be to Allaah.
Allaah says (interpretation of the meaning):
“Help you one another in Al-Birr and At-Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression’ [al-Maa’idah 5:2]
So it is not permissible for a Muslim to help anyone in doing anything that involves sin and transgression and violating the limits set by Allaah. So if a Muslim is in a position where he has the choice and it is easy for him to find someone who sells only halaal foods and keeps away from haraam things such as pork etc., then he should deal with that person and not with the one who sells both halaal and haraam such as pork, alcohol and so on. But if that is not possible, then it is permissible for the Muslim to buy halaal meat and permissible foods from him so long as the distinction between what is halaal and what is haraam is clear, because Allaah says (interpretation of the meaning):
“So keep your duty to Allaah and fear Him as much as you can “ [al-Taghaabun 64:16]
And Allaah is the source of strength. May Allaah bless our Prophet Muhammad and his family and companions, and grant them peace.