Being of service to others leads to happiness. In an authentic hadith, the Prophet (Blessings and Peace be upon him) said:
"Verily, Allah will say to His slave as He is taking account of him on the Day of Judgment, 'O' son of Adam, I was hungry and you did not feed me? He will answer, 'How can I feed you and you are the Lord of the worlds!' He will say, ‘Did you not know that my slave so and so who is the son of so and so felt hunger, and you did not feed him. Alas! Had y0u fed him you would have found that (i.e. reward) with Me. O’ son of Adam, I was thirsty and you gave me nothing to drink. He will say, ‘How can I give you drink, and you are the Lord of the worlds!” He will say, ‘Did you not know that my slave so and so, the son of so and so felt thirsty and you did not give him drink. Alas! If you had given him, you would have found that (i.e. reward) with Me. O’ son of Adam, l became sick and you did not visit Me.” He will say, “How can I visit you and you are the Lord of the worlds!” He will say, “Did you not know that my slave so and so, the son of so and so became sick and you did not visit him. Alas! Had you visited him, you would have found me with him."’
Here is an interesting point, in the last third of the hadith are the words: "...you would have found Me with him."
This is unlike the first two parts of the hadith: "You would have found that (i.e. the reward for feeding and giving drink) with Me."
The reason for the difference is that Allah, the Allah-Merciful, is with those whose hearts are troubled, as is the case with the person who is sick. And in another hadith, the Prophet (bpuh) said:
“There is reward in each moist liver (i.e. to do service to any living creature will be rewarded)."
Also, know that Allah admitted the prostitute from the children of Israel into Paradise because she gave a drink to a dog that was thirsty. So what will be the case for the one who feeds other humans, giving them drink and removing from them hardships! In an authentic hadith, the Prophet (bpuh) said,
"Whoever has extra provision should give from it to the one who has no provision. And whoever has an extra mount should give with this extra to the one who has no mount.”
Commanding his servant to search out for guests, Hatim said in some of his more beautiful verses:
"Burn the coals, for truly, the night is chilly,
If you bring me a guest, then I have set you free.”
And he said to his wife:
"Whenever you make food, then search for he who is hungry, as I do not eat alone."
Ibn Mubarak’s neighbor was a Jew. He would always feed him before feeding his own children and would provide clothing for him first and then for his children. Some people said to the Jew, “Sell us your house." He answered, "My house is for two thousand dinars. One thousand is for the price of the house and one thousand is for having Ibn Mubarak as a neighbor!" Ibn Mubarak heard of this and he exclaimed, "O’ Allah, guide him to Islam." Then, by the permission of Allah, he accepted Islam.
On another occasion, Ibn Mubarak passed by a caravan of people who were traveling to make the pilgrimage to Makkah, and he too was on his way to do the same. He saw one of the women from the caravan take a dead crow from a cesspit. He sent his servant to inquire about this and when he asked her, she replied, "We have had nothing for three days except that which finds its way into it." When Ibn Mubarak heard of this, his eyes swelled with tears. He ordered for all of his provision to be distributed among those of the caravan, and having nothing with which to continue the journey, he returned to his home and gave up making the pilgrimage for that year. Later, he saw someone in a dream saying, "Your pilgrimage has been accepted, as have your rites; and your sins have been forgiven."
(And give them preference over themselves, even though they were in need of that themselves) (Quran 59: 9)
One poet said:
"Even if I am a person who is far, from his friend in terms of distance,
I offer him my help and wish to alleviate his difficulties, And I answer his invitation and his call to me for help, And if he dons a wonderful new outfit I will not say, Alas, were I to be blessed with the clothes that he wears."
By Allah, how wonderful are good manners and a generous soul!
No one regrets having done well even if he was extravagant in doing so. Regret is only for the mistake or for the wrong done, even when that wrong is a minor one.