I went to donate blood in a hospital. A brother from the patient's side arranged good food for me. He sometimes insisted me to choose any food. So, I decided. And after blood donation, he managed the transportation. He dropped me at my home. When I was at the gate of my house, he gave me a good amount of money. I did not want to take this but he put it in my hand and insisted. He said to me, "Have some fruits purchased." So, was it permissible?
Selling is considered when you deliberately give someone something ONLY IN EXCHANGE for a return. In this case, he gave you the money of his own free will without you requesting it. In this case, in which he gave it to you of his own free will because of the good you did it is considered a Hadiyah (translates to gift) which in fact is a Sunnah to receive. The Prophet (PBUH) did not deny gifts.
It was narrated that the Prophet (PBUH) said:
“Come to the invitation, do not reject the gift, and do not abuse the Muslims.” (Narrated by Ahmad, Ibn Abi Syaibah, Al Bukhari in Adabul Mufrad and Shahihul Jami ‘Ash Shaghir )
“If I were invited to a meal of a sheep’s foot I would accept, and if I were given a sheep’s foot as a gift, I would accept.” (Narrated by al-Bukhaari (5178))."
One last one to strengthen my point even more:
Indeed, his acceptance of gifts was one of the signs of his Prophethood for the people who followed previously-revealed Books. Salmaan al-Faarisi (may Allaah be pleased with him) recognized him by that, as is told in the story of how he came to Islam, as narrated in the Musnad of Imam Ahmad (5/441)
I'll draw an analogy here and finish off my answer Insha Allah.
Consider it like this, you help walk an elderly person across the road just for the sake of Allah. If they give you a reward in return, it is considered Hadiyah. You did not require them before helping that I'll have $10 for helping you, they gave it to you because they were pleased with you. The exact same example applies in this case, it doesn't matter if what you helped them with was blood, finance, walking across the street, etc. As long as what you did, was to actually help them in a Halal manner (in this case, fighting some deadly blood disease, etc.) then it is alright for you to keep the gift if they gave it to you due to their pleasure and without you expecting it from them in the first place.
So it in fact seems like a reward from Allah for your act, may he bless you more.
One more tip: It is also believed by some scholars that if you do like the gift, then keep it, if you do not, give it away in Sadaqah. Utilizing a gift (Eating food, wearing clothes, spending money, etc.) and doing Sadaqah are both Sunnah, so both are rewarded by Allah (SWT).
And Allah knows the best.
It is impermissible to take reward/money for blood donation
There is an agreement among Muslim jurists on the impermissiblity of selling blood. The Quran explicitly declares:
Forbidden to you is [the consumption of] carrion, and blood… (Al-Ma’idah 5:3)
Say, ˹O Prophet,˺ “I do not find in what has been revealed to me anything forbidden to eat except carrion, running blood, swine—which is impure—or a sinful offering in the name of any other than Allah. But if someone is compelled by necessity—neither driven by desire nor exceeding immediate need—then surely your Lord is All-Forgiving, Most Merciful.” (6:145)
The Messenger of Allah (peace be upon him) sets a rule that dictates “When Allah forbids people to eat something, He forbids its price for them as well.”
Narrated Ibn Abbas:
I saw the Messenger of Allah sitting neat the Black stone (or at a corner of the Ka`bah). He said: He (the Prophet) raised his eyes towards the heaven, and laughed, and he said: May Allah curse the Jews! He said this three times. Allah declared unlawful for them the fats (of the animals which died a natural death); they sold them and they enjoyed the price they received for them. When Allah declared eating of thing forbidden for the people, He declares it price also forbidden for them.” (Abu Dawud) graded Saheeh by Albani
Narrated Awn ibn Abu Juhaifah:
My father bought a slave who practiced the profession of cupping. (My father broke the slave’s instruments of cupping). I asked my father why he had done so. He replied, “The Prophet forbade the acceptance of the price of a dog or blood, and also forbade the profession of tattooing, getting tattooed and receiving or giving Riba, (usury), and cursed the picture-makers.” (Al-Bukhari)
Al-Haafiz said in al-Fath:
What is meant by the prohibition of blood is the same as the prohibition of dead meat and pork. It is haraam according to scholarly consensus, i.e., selling blood and taking its price.
How to dispose the blood donation reward
The best way to dispose of the (forcefully) given reward/money to you for blood donation is to give it to a poor person, charity or a sound organization. In this way you do not need to argue with the reward-er and would not consume haram.
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