'Umar was heard to say, "Anyone who does not show mercy will not be shown mercy. Anyone who does not forgive will not be forgiven. Anyone who does not turn in repentance will not be turned to nor will he be protected or guarded."  

عَنْ عُمَرَ قَالَ لاَ يُرْحَمُ مَنْ لاَ يَرْحَمُ وَلاَ يُغْفَرُ لِمَنْ لاَ يَغْفِرُ وَلاَ يُتَابُ عَلَى مَنْ لاَ يَتُوبُ وَلاَ يُوقَّ مَنْ لا يُتَوَقَّ  

Mu'awiya ibn Qurra reported that his father said, "A man said, 'Messenger of Allah, I was going to slaughter a sheep and then I felt sorry for it (or 'sorry for the sheep I was going to slaughter').' He said twice, 'Since you showed mercy to the sheep, Allah will show mercy to you.'"  

قَالَ رَجُلٌ يَا رَسُولَ اللهِ إِنِّي لَأَذْبَحُ الشَّاةَ فَأَرْحَمُهَا أَوْ قَالَ إِنِّي لَأَرْحَمُ الشَّاةَ أَنْ أَذْبَحَهَا قَالَ وَالشَّاةُ إِنْ رَحِمْتَهَا رَحِمَكَ اللَّهُ مَرَّتَيْنِ  

Abu Hurayra said, "I heard the Prophet, may Allah bless him and grant him peace, the truthful confirmed one, Abu'l-Qasim, may Allah bless him and grant him peace, say, 'Mercy is only removed from the one who is destined for wretchedness."  

سَمِعْتُ النَّبِيَّ ﷺ الصَّادِقَ الْمَصْدُوقَ أَبَا الْقَاسِمِ ﷺ يَقُولُ لاَ تُنْزَعُ الرَّحْمَةُ إِلا مِنْ شَقِيٍّ  

Jarir reported that the Prophet, may Allah bless him and grant him peace, said, "Allah will not show mercy to a person who does not show mercy to other people."  

عَنِ النَّبِيِّ ﷺ قَالَ مَنْ لا يَرْحَمُ النَّاسَ لا يَرْحَمُهُ اللَّهُ