To do an act of kindness is a branch of compassion, or, rather, its fruit. It can have many forms, such as, the doing someone a favour, the offering a gift, or the rendering a service or acting in any other manner that may be a source of joy or comfort to anyone. The holy Prophet Sallallahu alaihe wasallam has urged upon his followers to make all these part of their social and moral behaviour.
Anas radiallahu anhu related to us that the Messenger of Allah Sallallahu alaihe wasallam said: "He who fulfils the need of any of my people to make him happy, truly makes Me happy. And, he who makes me happy, in fact, makes Allah happy, and, he who makes Allah happy, Allah will make him enter Paradise." (Baihaqi)
It tells that a true Believer should always be kind-hearted and amiable to others and an act of goodness should not be done only to those who are good to us, but to such people, as well, who treat us unjustly. We can see how much the Messenger of Allah Sallallahu alaihe wasallam cares for his people from the above hadith. If anyone pleases another person by doing something for him then he pleases the Prophet Sallallahu alaihe wasallam and thereby earns the pleasure of Allah and Paradise.