The most merciful of those in the earth Al-Adab Al-Mufrad 372
Arabic hadith text
حَدَّثَنَا حَفْصُ بْنُ عُمَرَ، قَالَ: حَدَّثَنَا شُعْبَةُ، عَنْ عَبْدِ الْمَلِكِ بْنِ عُمَيْرٍ، عَنْ قَبِيصَةَ بْنِ جَابِرٍ، عَنْ عُمَرَ قَالَ: لاَ يُرْحَمُ مَنْ لاَ يَرْحَمُ، وَلاَ يُغْفَرُ لِمَنْ لاَ يَغْفِرُ، وَلاَ يُتَابُ عَلَى مَنْ لاَ يَتُوبُ، وَلاَ يُوقَّ مَنْ لا يُتَوَقَّ.
Translation
'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."