The first thing to purify is the abdomen, so eat Halal food.
Sahih al-Bukhari 7152
Full Hadith
حَدَّثَنَا إِسْحَاقُ الْوَاسِطِيُّ، حَدَّثَنَا خَالِدٌ، عَنِ الْجُرَيْرِيِّ، عَنِ طَرِيفٍ أَبِي تَمِيمَةَ، قَالَ شَهِدْتُ صَفْوَانَ وَجُنْدَبًا وَأَصْحَابَهُ وَهْوَ يُوصِيهِمْ فَقَالُوا هَلْ سَمِعْتَ مِنْ رَسُولِ اللَّهِ صلى الله عليه وسلم شَيْئًا قَالَ سَمِعْتُهُ يَقُولُ ” مَنْ سَمَّعَ سَمَّعَ اللَّهُ بِهِ يَوْمَ الْقِيَامَةِ ـ قَالَ ـ وَمَنْ يُشَاقِقْ يَشْقُقِ اللَّهُ عَلَيْهِ يَوْمَ الْقِيَامَةِ ”. فَقَالُوا أَوْصِنَا. فَقَالَ” إِنَّ أَوَّلَ مَا يُنْتِنُ مِنَ الإِنْسَانِ بَطْنُهُ، فَمَنِ اسْتَطَاعَ أَنْ لاَ يَأْكُلَ إِلاَّ طَيِّبًا فَلْيَفْعَلْ، وَمَنِ اسْتَطَاعَ أَنْ لاَ يُحَالَ بَيْنَهُ وَبَيْنَ الْجَنَّةِ بِمِلْءِ كَفِّهِ مِنْ دَمٍ أَهْرَاقَهُ فَلْيَفْعَلْ ”. قُلْتُ لأَبِي عَبْدِ اللَّهِ مَنْ يَقُولُ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم جُنْدَبٌ قَالَ نَعَمْ جُنْدَبٌ.
Narrated Tarif Abi Tamima:
I saw Safwan and Jundab and Safwan’s companions when Jundab was advising. They said, “Did you hear something from Allah’s Messenger (ﷺ)?” Jundab said, “I heard him saying, ‘Whoever does a good deed in order to show off, Allah will expose his intentions on the Day of Resurrection (before the people), and whoever puts the people into difficulties, Allah will put him into difficulties on the Day of Resurrection.'” The people said (to Jundab), “Advise us.” He said, “The first thing of the human body to purify is the `Abdomen, so he who can eat nothing but good food (Halal and earned lawfully) should do so, and he who does as much as he can that nothing intervene between him and Paradise by not shedding even a handful of blood, (i.e. murdering) should do so.”
Lesson
As dutiful Muslims, we should decide what we eat with caution. If a food is doubtful, it is better not to eat it since there’s a possibility of it being haram. It is said that when someone eats something haram, their prayers are not accepted for 40 days, thus emphasizing the significance of being 100% sure that what we eat is halal.