Sahih Adab al-Mufrad

It is narrated from Abu Ajlan Muharibi who said: I was in the army of Abdullah bin Zubair. One of my paternal cousins passed away, and he had made a will to give a camel in the way of Allah. I said to his son, "Give me the endowed camel because I am part of Abdullah bin Zubair's army." He said, "Come with me to Abdullah ibn Umar (may Allah be pleased with them both) so that we may ask him for a fatwa." We went to Abdullah ibn Umar (may Allah be pleased with them both). He (the son) said to Ibn Umar: "O Abu Abdur Rahman! My father has passed away, and he made a will to give one of his camels in the way of Allah. And this is my cousin, and he is part of Ibn Zubair's army. Should I give him this camel?" Abdullah ibn Umar (may Allah be pleased with them both) said: "O my son! 'The way of Allah' refers to every good deed. If your father made a will to give his camel in the way of Allah, then when you see a group of Muslims fighting in jihad against a group of polytheists, give the camel to those Muslims. And this man and his companions are fighting in the way of the children of the nation (not in the way of Allah), to see which of them gains power."

Sayyiduna Jarir (may Allah be pleased with him) narrates from the Prophet (peace and blessings of Allah be upon him) that whoever does not show mercy to people, Allah the Exalted will not show mercy to him.

It is narrated from Sayyiduna Umar (may Allah be pleased with him) that he said: Whoever does not show mercy will not be shown mercy; whoever does not forgive will not be forgiven; whoever does not pardon will not be pardoned; whoever does not accept repentance will not have his repentance accepted; and whoever does not protect himself from sin will not be protected.