Allah, the Wise, has said:
وَ يُوثِرُونَ عَلىَ اَنْفُسِهِم وَ لَوْ كاَنَ بِهِم خَصاَصَةٌ
"And prefer (the Mohajirs) over themselves though poverty may afflict them." 
The Holy Prophet (s.a.w.) said:
اَيُّما اِمرِئٍ اِشتَهىَ شَهوَةً فَرَد شَهوَتَهُ وَ آثَرَ عَلىَ نَفسِهِ غُفِرَ لهُ
"One, who covets something, (but) suppressing his desire gives others preference over himself, shall have his sins forgiven." 
The highest degree of generosity and munificence is altruism. An altruistic person, despite having his own acute needs and necessities, makes a sacrifice by giving others preference over himself.
Even the act of giving alms occupies a lower rank than altruism. Attaining the pleasure of Allah plays a pivotal role in it. If a person, in an effort to save the life of a drowning person, gets drowned himself, the commendation from the Lord for this self-sacrifice, is a thousand times more than that for the alms which he pays out.
1 - The Altruistic Slave
A'bdullah Ibn Ja’far, the husband of Hadhrat Zainab (a.s.) was a person whose generosity was unparalleled. Once, as he happened to pass by a palm-plantation, he noticed a slave working there. At that very moment, the slave’s food was brought and handed over to him. As he was about to start his meal, a hungry dog came before him, wagging its tail.
The slave placed a portion of his food before the dog and the animal immediately ate it up. The slave put some more food in front of the dog and before long it was eaten too. This continued till he had given his entire food to the dog.
A'bdullah, who had been witnessing the incident, asked the slave, "What is your daily ration of food?"
"The amount which you have just witnessed," the slave answered.
"If that is the case, why then did you give the dog preference over yourself?" enquired A’bdullah.
"This dog had come from afar and was hungry and I did not deem it appropriate to drive him away in that state of hunger."
"With what will you satiate yourself today?"
"I shall overcome my hunger by patience and steadfastness," the slave explained.
A'bdullah, observing the slave’s selflessness and altruism, thought to himself that the slave was more generous than himself. By way of commendation and compensation for his altruism, A’bdullah purchased the slave and the plantation from the owner, freed the slave and finally gifted the entire plantation to him.
2 – The Incident of the Mosque of Merv
Abu Muhammad Azdi narrates:
When the mosque of Merv caught fire, the Muslims assumed that it was the work of the Christians and retaliated by setting their houses ablaze.
When the king came to know of this act, he ordered those involved in the incident to be arrested and punished. He ordered that the culprits should face one of three types of punishment - death, severing of a hand or whipping. Each punishment was to be written on a small piece of paper which was then placed in a box. Every guilty person was required to draw a piece from the box and would be subjected to the punishment written on it.
When one of these people picked and read his paper, he broke down in tears because his sentence was the death penalty.
A young boy, who appeared to be happy as he was to be punished with lashes, asked the distressed person:
"Why are you agitated and weeping? These punishments should not be a problem in the path of serving the religion."
The first person responded, "We have served our religion and therefore do not fear death, but the truth is that I have an old mother, and since I am her only son, she is entirely dependant upon me. When she hears about my death, she will not survive."
Having heard this, the youth reflected for a while and then said, "Neither is my mother alive nor do I have an attachment with anyone. Let us exchange our punishment so that I get killed instead of you and you face the lashes, after which you can return home to care for your mother."
The two exchanged their punishment; the youth was killed, while the other person, after being lashed, returned home to his mother.
3 – The Battle of Yarmuk (Tabuk)
In the battle of Yarmuk, a group of Muslim soldiers would go out for battle everyday. After a few hours of confrontation, the unhurt and those who had minor injuries would return, while the wounded or dead would be left on the battlefield.
Hudhaifah U’dwi, recounts:
One day, my cousin, together with some other soldiers, set out for the battlefield. Unfortunately, after the conclusion of the day’s battle, he failed to return. Picking up a container of water, I set out for the battlefield, hoping to provide him with a drink in case he happened to be alive.
After searching for sometime, I found my cousin who was barely alive. I stooped down beside him and asked him if he needed some water. He nodded. At that very moment, another soldier, who lay near him, heard me and then sighed loudly to indicate that he was very thirsty.
My cousin signalled to me to provide water to the soldier first. As I went to attend to the injured soldier, I realized that he was Hishaam Ibn A’as. I asked him whether he needed water.He signalled in the affirmative. Instantaneously, another injured soldier demanded water and Hishaam too refused to drink the water before the other soldier had drunk it. I moved towards the third soldier, but just as I reached him, he breathed his last. Returning to Hishaam, I observed that in this ensuing period, he too had died. I hastened towards my cousin, only to find him dead too!
4 – A'li (a.s.) in Place of the Holy Prophet (s.a.w.)
When the leaders of Quraish realised that the inhabitants of Madinah had pledged their loyalty to the Prophet, their hatred towards him intensified. Consequently, their leaders decided that on the eve of the first of Rabi’ al-Awwal, one brave person from every tribe would gather together, besiege the Prophet’s house and kill him as he lay asleep in his bed.
God divulged their sinister plan to the Prophet, who said to Amirul Mu'mineen (a.s.):
"As the polytheists intend to murder me tonight, God has ordered me to migrate. Will you sleep in my place so that they do not find out that I have gone?"
"O’ Prophet of Allah! Will you remain alive and well if I do this?" A’li (a.s.) asked.
The Holy Prophet (s.a.w.) confirmed that he would. Hearing this, Amirul Mu’mineen’s (a.s.) face lit up with delight and he fell down in prostration of thanksgiving (to the Almighty Lord). He then said, "May my life be sacrificed for you! Go wherever God has ordered you to go; if you need me to do any work for you, just command me, and I shall unconditionally perform it, and from God I seek grace and success."
The Holy Prophet (s.a.w.) took A'li (a.s.) in his arms, wept profusely and entrusted him to the protection of Allah. Then, Jibraeel took the Holy Prophet (s.a.w.) by the hand and led him out of the house and towards the cave of Thaur.
That night, Amirul Mu'mineen slept in the Holy Prophet’s (s.a.w.) bed and covered himself with his cloak.
The infidels had initially intended to attack the house in the darkness of the night, but Abu Lahab, who was also with them, advised against it saying that it was night and the women and children were asleep. He told them to wait till morning. When morning dawned, they rushed into the house only to find A'li (a.s.) in the Prophet’s bed. They asked him where Muhammad was.
"Did you leave him with me (that you now ask me about him)? You wanted to get rid of him (and so) he has gone away himself," he retorted.
They left A'li (a.s.) and set off in pursuit of the Holy Prophet (s.a.w).
However, it was as a result of this act of self-sacrifice on the part of A'li (a.s.), that the Holy Prophet (s.a.w.) remained alive and unharmed. God revealed the following verse on this occasion. It pertains to Ali (a.s.)
And among men is he, who sells himself to seek the pleasure of Allah; and Allah is Affectionate to the servants.
5 – The Self-Sacrifice of Haatim Taai
Once, there was a severe famine in the place where Haatim Taai was staying. The provisions had dwindled until there was nothing left and the people were suffering intense hunger and hardship.
Haatim’s wife narrates:
One night, there was not a morsel to be found in our house. Haatim, my two children, A’di and Safaanah and myself, found that we could not sleep due to our hunger.
With great difficulty, Haatim put A’di to sleep while I did likewise with Safaanah. Haatim then began to narrate a story with the intention of putting me to sleep, but the intensity of hunger kept me awake. All the same, I pretended to be so fast asleep that even when he called out to me several times, I did not reply back.
Haatim had been gazing into the desert from a hole in the tent, when he noticed a silhouette, advancing towards us. As it came nearer, Haatim realised that it was a lady and called out:
"Who is it?"
The lady bemoaned, "Haatim, my children are howling like wolves owing to their hunger."
Haatim told the woman not to worry, as he would remove their hunger. Hearing this, I got up from my place and asked him how he would do it.
He said, "I shall feed every one."
He then proceeded towards the only horse which we possessed and which we utilized to transport our belongings. He sacrificed it and gave a portion of it to the lady saying:
"Cook it and feed it to your children." Turning to me, he said, "Awaken the children so they can eat too."
After a short while, he added, "It is a great shame to eat while others sleep beside you with an empty stomach."
He proceeded to wake them up himself. Everyone ate the meat, except Haatim, who sat and derived pleasure out of watching them eat.
 Holy Qur'an, ch. Al-Hashr (59), vs. 9.
 Jaame' al-Sa'adaat, vol. 2, pg. 118.
 Hikaayat-ha-e-Shanidani, vol. 5, pg. 114; Al-Mahajjah al-Baidhaa, vol. 6, pg. 80.
 Namunah-e-Ma'arif, vol. 2, pg. 435; Mustatraf, vol. 1, pg. 157.
 Daastaan-ha Wa Pand-ha, vol. 1, pg. 173; Mustatraf, vol. 1, pg. 156.
 The Holy Prophet (peace be upon him and his holy progeny) remained in the Cave of Thaur for three days and on the fourth day proceeded towards Medinah, entering it on the 12th of Rabi’ al-Awwal in the 13th year after the proclamation of Prophethood, and from this migration commenced the Islamic calendar.
 Holy Qur'an, ch. Al-Baqarah(2), vs. 207.وَ مِنَ النَاَسِ مَن يَّشْرٍي نَفْسَهُ ابْتِغاَءَ مَرْضاَتِ اللهِ وَ اللهُ رَؤُفٌ بِالْعِباَد
 Raahnama-e-Sa’adat, vol. 2, pg. 350; Safinah al-Bihaar, vol. 1. pg. 208.