The Prophet once kissed Al-Hassan ibn 'Ali, may Allah be pleased with him, while Al-Aqra' ibn Haabis was in his presence. So Al-Aqra', may Allah be pleased with him, said to him: "Do you kiss your children? I swear by Allah, I have ten children but I have never kissed any one of them!" Thereupon, the Prophet said: "Whoever is not merciful will not be treated mercifully." [Muslim]
Verily, in Islam, mercy encompasses this world and the Hereafter, as well as humankind, animals, birds and the surrounding habitats. Allah Says (what means): "And My Mercy encompasses everything." [Quran 7:156]
Allah has ascribed Mercy to Himself and He has also described His Prophets, may Allah exalt their mention, and righteous servants as being endowed with it. Allah Says (what means): "Muhammad is the Messenger of Allah and those who are with him are severe against the disbelievers and merciful to one another." [Quran 48:29]
Allah has made his sending forth of the Prophet as a mercy to all of creation, as He Says (what means): "And We have not sent you (O Muhammad) except as a mercy to the worlds." [Quran 21:107] The word "worlds" ('Aalameen) is general and includes the world of the humans, the world of the Jinn, the world of the animals, the world of the birds, as well as the nations found on land and in the sea.
Allah has commanded that mercy be applied to everything and in every action. Thus, even when you slaughter a sacrificial animal, you show mercy to it by saying ‘Bismillaah’ (In the name of Allah) and by sharpening your knife (so that it will be a quick and painless death). The Prophet said: "Verily Allah has prescribed Ihsaan (goodness) for everything. So when you slaughter, 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."
It is reported that Allah forgave a prostitute from the children of Israel who showed mercy to a dog that was dying from thirst. She filled her shoe with water and then taking hold of the dog's mouth, she gave it the water to drink. Allah appreciated what she did and forgave her sins.
Once our Prophet saw that one of his Companions, may Allah be pleased with him, grabbed the chick of a lark, and it began screeching over the heads of the Companions, may Allah be pleased with them. So he said: "Who bereaved this (lark) of her child? Return her children back to her!"
The weaker and poorer a human being is, the more we are required to show mercy to him and be gentle with him. This is why our Lord has forbidden us from oppressing the orphan. Allah Says (what means): "Therefore, treat not the orphan with oppression. And do not repel the beggar." [Quran 93: 9-10]
The Prophet 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." He would rub the head of the orphans and say: "I and the guardian of an orphan will be like this in Paradise - and he gestured with his index and middle finger."
Indeed the Prophet commanded us to take care of the children, women and the elders. Thus, in his last words to his Companions, may Allah be pleased with them, and his nation, he said: "The prayer and whatever your right hands possess." "Take good care of the women (i.e. wives)." And he said: "The best of you is the best to his wives. And I am the best amongst you to my wives."
Mercy is something innate, which Allah has placed into the hearts of His creatures, even the lions -- the most ferocious of beasts -- are merciful to their children. Yet, Allah is more merciful to His creation than a mother to her child. It is reported that on the day that Allah created mercy, He created one hundred parts of it. He left ninety-nine parts with Him, by which He will show mercy to His servants on the Day of Judgment and He sent down one single part of mercy to the Earth, which humans and animals share amongst themselves.
The Messenger of Allah has condemned the person that is void of any mercy, and he condemned the one who breaks family ties. He said: "Kinship is connected to the Throne ('Arsh). It says: 'Whoever severs me, then Allah will break (away from) him. And whoever maintains me, then Allah will keep connected to him."
In another narration he said: "Verily, the kinship will be connected to the Throne of the Most Merciful on the Day of Judgment. 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.'"
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. Ar-Raheem). This is why He has commanded it in every place and in every situation. A Muslim begins his action by saying ‘Bismillaahir-Rahmaanir-Raheem’ (in the name of Allah, the Most Merciful, the Giver of Mercy) so that Allah can bless him in his action. Every action that is devoid of mercy has no blessing in it, nor does it have any good. If the servants of Allah show mercy towards one another, this is a cause for Allah sending His mercy down on them.
The Prophet 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 were merciful. And have mercy on our dead ones and put those who have mercy from amongst Your Servants in charge over us, O Most Merciful!