Benevolence is a principal characteristic of the true Muslim, and offering good gratuitously to others is highly recommended in the Qur’an and the Sunnah. How many a time people become subject to lack of blood, such as in the case of medical surgeries or car accidents, and every Muslim should offer what he or she is able to give for them, as long as there is no subsequent harm on his or her part.

In response to your question, Dr. `Ali Jumu`ah, the current Mufti of Egypt, stated,

Allah, the Almighty, has honored people and favored them over the rest of His creatures. He, Exalted be He, prohibited them from inflicting harm on themselves or violating their sanctity.

In addition, one of the main objectives of the Shari`ah is the preservation of the human soul. Allah, the Almighty, says, (Verily we have honored the Children of Adam. We carry them on the land and the sea, and We have made provision of good things for them, and We have preferred them above many of those whom We created with a marked preferment.) (Al-Israa‘ 17:70)

Among the manifestations of Allah’s favors upon humans is that He created them in the best and most beautiful form. Man should be thankful to Allah for that. Almighty Allah says, (Surely We created man of the best stature.) (At-Tin 95:4)

The human body is a trust for which man is responsible, and therefore it is impermissible to tamper with it. Thus, all the divine laws prohibited killing and suicide and whatever leads to them. He, Exalted be He, says, (And cast not yourselves to perdition with your own hands, and do good (to others); surely Allah loves the doers of good.) (Al-Baqarah 2:195)

(And do not kill your people; surely Allah is Merciful to you.) (An-Nisaa’ 4:29)

Abu Huraira narrated that the Messenger of Allah (peace and blessings be upon him) said, “O servants of Allah! Seek medical treatment, because Allah did not make a disease without making a cure for it, save old age.” (Al-Bukhari and Muslim) In another narration of the hadith, the Prophet said, “Allah did not make a disease without making a cure for it, save death.

It is permissible to donate blood if qualified, trustworthy physicians determine the following:

• It will save the recipient from certain harm.

• It must not harm the donor’s health or quality of life.

This is based on the juridical permissibility to save another’s life as Allah has ordained and the encouragement to be altruistic, as attested to by the following Qur`anic verse, (And prefer (them) before themselves though poverty may afflict them, and whoever is preserved from the niggardliness of his soul, these it is that are the successful ones.) (Al-Hashr 59:9)

Permissibility of blood donations is based on the analogy of saving people from drowning, burning, or being buried under a collapsed building, all of which cases involve the potential harm for the person trying to save them.

Allah, the Almighty, says: (And help one another in goodness and piety, and do not help one another in sin and aggression.) (Al-Ma’idah 5:2)

• Surely, Allah rewards the legally competent and healthy person who donates his or her blood to save another. He will either raise his or her rank or forgive him or her bad deeds. Allah, the Almighty, says, (Is the reward of goodness aught but goodness?) (Ar-Rahman 55:60)

• The Prophet said, “Muslims are brothers to one another. Allah fulfills the needs of whoever fulfills the needs of a fellow Muslim. A Muslim does not oppress a fellow Muslim, nor does he hand him over to an oppressor. Whoever relieves a burden from a fellow Muslim, Allah will relieve him of one of the burdens of the Day of Judgment. And whoever covers [a fault] for a Muslim, Allah will cover for him on the Day of Judgment.” (Al-Bukhari)

• The Prophet said, “Whoever relieves the distress of a Muslim in this life, Allah will relieve him of a distress on the Day of Judgment; whoever facilitates a Muslim’s difficulty, Allah will facilitate his difficulties in this world and in the hereafter; whoever conceals the faults of Muslim, Allah will conceal his faults in this world and in the hereafter. Allah will help whoever helps a fellow Muslim.” (Abu Dawud)

There is nothing wrong with donating blood, provided that the following conditions are observed before donating:
1. There should be an overwhelming necessity to that, such as donating blood to the victims of accidents and catastrophes and those undergoing surgery.

2. Blood donations must be of medically asserted benefits and preventing harm.

3. Physicians must determine that such a donation will not prevent the donor from pursuing his life in a normal manner.

4. Medical tests must prove that the donor is free from diseases. This is because of the legal rule, “harm is not to be removed by another.”

5. The donor must be legally competent.

Excerpted with slight modifications from Dar-alifta.org