Verily, mercy - in our religion - encompasses this world and the hereafter, as well as mankind, animals, birds, and the surrounding habitats.
Allah says: "And My mercy encompasses everything."
Allah has described Himself with mercy and He has also described His prophets and righteous servants with it. Allah says: "Muhammad is the Messenger of Allah (saws) and those who are with him are severe against the disbelievers and merciful to one another."
Allah has made his sending forth of the Prophet (saws) as a mercy to all of creation, as He says: "And We have not sent you (O Muhammad) except as a mercy to the worlds."
The word "worlds" (`aalameen) is general and thus includes the world of the humans, the world of the jinn, the world of the animals and the world of the birds, as well as the nations found on land and the nations found on sea.
And indeed Allah has commanded that mercy be applied to every thing and in every action. So even when you slaughter you sacrificial animal, you show mercy to it by saying Bismillaah and by sharpening your sword (so that it will be a quick and painless death). The Prophet (saws) said: "Verily Allah has prescribed Ihsaan (goodness) for everything. So when you slaughter, then slaughter in a good manner, and when you kill (in war), then kill in a good manner. And let each of you sharpen his blade and let him spare the animal he slaughters from suffering."
And once our Prophet (saws) saw one of his Companions grab the baby of a lark, and it began screeching over the heads of the Companions. So he (saws) said: "Who bereaved this (lark) of her child? Return her children back to her!"
The more weak and poor a human being is, the more required we are of showing mercy to him. And being gentle with him is what is most incumbent. This is why our Lord has forbidden us from oppressing the orphan. Allah says: "Therefore, treat not the orphan with oppression. And do not repel the beggar."
The Prophet (saws) said: "The person that looks after and supports the widow and the needy one is like the mujaahid (one who makes Jihaad) in the Cause of Allah."
And he (saws) would rub the head of the orphan and say: "I and the guardian of an orphan will be like this in Paradise - and he SAWS gestured with his index and middle finger."
Indeed he (saws) commanded us to take care of the children and the women and the elders. Thus, in his last words to his Companions and his nation, he said: "The prayer and what your right hands possess." "Take good care of the women (i.e. wives)." And he (saws) said: "The best of you is the best to his wives. And I am the best amongst you with my wives."
Mercy is something innate, which Allah has placed into the hearts of (all) His creatures, even the lions - the most dangerous of them - for they are merciful to their children. Yet Allah is more merciful to His creation than a mother is to her child. That is why on the day that He created mercy, He created one hundred parts to it. And He left ninety-nine parts with Him, by which He will show mercy to His servants on the Day of Judgement, and sent down one single part of mercy to earth, which humans and animals share amongst themselves.
The Messenger of Allaah (saws) has condemned the person that is void of any mercy and who doesn't attain a large amount of it. This is why he (saws) condemned the one who breaks family ties. He (saws) said: "Kinship is connected to the Throne (`Arsh). It says: `Whoever severs me, then break (away from) him. And whoever maintains me, then keep connected to him."
And in one narration: "Verily, the kinship will be connected to the Throne of the Most Merciful on the Day of Judgement. It will say: `This is the place for the one who sought refuge in You from the severing (of family ties).' So Allah will say to it: `Will it please you that I connect those who maintained you and that I cut off those who severed you?' And it will say: `I will be pleased (with that), my Lord.'"
And he (saws) condemned the oppressive leaders who do not show mercy to their people, by saying: "The worst leaders are the cruel oppressive ones (al-hutamah)."
And Allah has named Himself Ar-Rahmaan and Ar-Raheem, so he is the Most Merciful of this world and the Hereafter (i.e. Ar-Rahmaan) and the bestower and giver of mercy (i.e. Raheem). This is why He has commanded it in every place and in every situation. The Muslim begins his action by saying Bismillaahir-Rahmaanir-Raheem so that Allah can bless him in his action. So every action that is void of mercy, then there is no blessing in it, nor any good. And the servants of Allah showing mercy towards one another is a cause for Allah sending His mercy down on them.
The Prophet (saws) said: "The Most Merciful shows mercy to those who have mercy on others. Show mercy to those on earth, and the One above the heaven will show mercy to you."
O Allah, have mercy on us above the earth and below the earth and on the Day when our deeds will be presented to us. And cause us to be merciful to one another just as the Companions of Your Prophet (saws) were. And have mercy on our dead ones and put those who have mercy from amongst Your servants in charge over us O Rahmaan O Raheem!