I have read why Muslims can't eat certain foods, e.g.: pork, horse, donkey, sharks, and animals of prey (lions, tigers,etc.). But, I can't find why Muslims can't eat or drink blood. If that is the case, then eating any flesh is wrong, since all flesh contains blood, even if you drain off the excess, blood still remains in the tissue. I would like an answer to that question.
Blood which is liquid and flows is haram (prohibited) because of the command of the following verse of the Quran:
قُل لَّا أَجِدُ فِي مَا أُوحِيَ إِلَيَّ مُحَرَّمًا عَلَىٰ طَاعِمٍ يَطْعَمُهُ إِلَّا أَن يَكُونَ مَيْتَةً أَوْ دَمًا مَّسْفُوحًا أَوْ لَحْمَ خِنزِيرٍ فَإِنَّهُ رِجْسٌ أَوْ فِسْقًا أُهِلَّ لِغَيْرِ اللَّهِ بِهِ ۚ فَمَنِ اضْطُرَّ غَيْرَ بَاغٍ وَلَا عَادٍ فَإِنَّ رَبَّكَ غَفُورٌ رَّحِيمٌ
Say, "I do not find within that which was revealed to me [anything] forbidden to one who would eat it unless it be a dead animal or blood spilled out or the flesh of swine - for indeed, it is impure - or it be [that slaughtered in] disobedience, dedicated to other than Allah . But whoever is forced [by necessity], neither desiring [it] nor transgressing [its limit], then indeed, your Lord is Forgiving and Merciful."
The prohibition is specifically linked to blood that flows out when the animal has been Islamically slaughtered, i.e. by cutting the juglar veins and carotid arteries, and does not extend to trace amounts that remain in the flesh after being drained and washed etc.
Tafsir Qurtubi on 6:145 writes:
والمسفوح: الجاري الذي يسيل وهو المحرّم. وغيره مَعْفُوٌّ عنه. وحكى الماورديّ أن الدم غير المسفوح أنه إن كان ذا عروق يُجمد عليها كالكبد والطحال فهو حلال؛ لقوله عليه السلام: " أحِلّت لنا ميتتان ودمان " الحديثَ. وإن كان غير ذي عروق يجمد عليها، وإنما هو مع اللحم ففي تحريمه قولان: أحدهما أنه حرام؛ لأنه من جملة المسفوح أو بعضه. وإنما ذكر المسفوح لاستثناء الكبد والطحال منه. والثاني أنه لا يحرّم؛ لتخصيص التحريم بالمسفوح.
قلت: وهو الصحيح. قال عمران بن حُدير: سألت أبا مِجْلَز عما يتلطخ من اللحم بالدم، وعن القِدر تعلوها الحمرة من الدّم فقال: لا بأس به، إنما حرّم الله المسفوح. وقالت نحوه عائشة وغيرُها، وعليه إجماع العلماء. وقال عكرمة: لولا هذه الآية لاتبع المسلمون من العروق ما تتبع اليهود.
مسفوح means that which goes forth, and flows and this has been prohibited.
And that which does not do this is مَعْفُوٌّ عنه Mawari has narrated: The blood which does not flow out (non مسفوح ) and is in the blood vessels and has dried\solidified up in them, such as in the liver and spleen, then it is permissible since the Prophet said:
“Two kinds of dead meat and two kinds of blood have been permitted to us. The two kinds of dead meat are fish and locusts, and the two kinds of blood are the liver and spleen.” [ Narrated in Sunan Ibn Majah ]
And if it is not of the blood vessels, and has solidified on the meat, then there are two opinions about it:
One is that it is prohibited, because it is neither fully flowing nor otherwise. And for the permissibility of the liver and spleen flow has been mentioned.
The second view is that it is not prohibited, since the prohibition is specific on flowing. I say: This is correct. Imran bin Jarir said: I asked Abu Mujliz about meat which is covered [saturated] with blood and [when cooked] the food has its redness, and he said: There is no problem with it. Doubtless Allah has prohibited only blood that flows out. Similar was said by Ayesha and others and this is the concencus of the Ulema. Ikrimah said: If this verse was not revealed then we Muslims would have refrained the veins which the Jews refrained from.