Hazrat Moulana Muhammad Ilyaas (rahmatullahi ‘alaih) once mentioned the following:
Jannah is the reward that one receives in exchange for fulfilling huqooq (rights). In other words, when a person sacrifices his comfort and ease for the sake of Allah Ta‘ala, and endures difficulty in order to fulfill the rights that he owes to people (and Allah Ta‘ala), then in lieu of this, he is rewarded with Jannah.
The hadeeth mentions:
ارحموا من في الأرض يرحمكم من في السماء
Show mercy to those on earth, and the One in the heavens will show mercy to you.
In the Mubaarak ahaadeeth, we find two famous incidents mentioned regarding two women. One incident is regarding a loose, immoral woman who noticed that a dog was thirsty. She took pity on the dog, drew water from a well and gave it the water to drink. On account of her showing mercy to the dog, Allah Ta‘ala granted her Jannah.
The second incident is regarding a woman who was not involved in shameful actions, but she had a cat which she kept tied and deprived it of food and drink. In this way, she made it suffer and killed it through making it starve to death. Hence, on account of this cruel action, she will be flung into the fire of Jahannum.
Note: From the first incident, we understand that when one fulfils the rights that he owes to others and shows them kindness, then he is rewarded. On the contrary, when one does not fulfil the rights that he owes to Allah Ta‘ala and people, then he is worthy of punishment.
(Malfoozaat Hazrat Moulana Muhammad Ilyaas (rahmatullahi ‘alaih) pg. 19)