Umar on Zina: No right to punish the unborn child of adultery

Abu Sufyan reported: A man was absent from his wife for two years and he returned to find her pregnant. Umar, may Allah be pleased with him, came and he considered stoning her. Mu’adh said to him, “Even if you have a legal case against her, you have no case against what is in her belly.” Umar left her and she gave birth to a boy who clearly resembled his father. His front teeth came out and the man said, “This is my son.” Umar said, “If only women could give birth to the likes of Mu’adh! Were it not for Mu’adh, Umar would be ruined.”

Source: Tārīkh Dimashq 58/422

عَنْ أَبِي سُفْيَانَ أَنَّ رَجُلًا غَابَ عَنِ امْرَأَتِهِ سَنَتَيْنِ فَجَاءَ وَهِيَ حُبْلَى فَأَتَى عُمَرَ رضي الله عنه فَهَمَّ بِرَجْمِهَا فَقَالَ لَهُ مُعَاذٌ إِنْ يَكْ لَكَ عَلَيْهَا سَبِيلٌ فَلَيْسَ لَكَ عَلَى مَا فِي بَطْنِهَا سَبِيلٌ فَتَرَكَهَا فَوَضَعَتْ غُلَامَا بَانَ أَنَّهُ يُشْبِهُ أَبَاهُ قَدْ خَرَجَتْ ثَنْيَتَاهُ فَقَالَ الرَّجُلُ هَذَا ابْنِي فَقَالَ عُمَرُ عَجَزَتِ النِّسَاءُ أَنْ يَلِدْنَ مِثْلَ مُعَاذٍ لَوْلَا مُعَاذٌ لَهَلَكَ عُمَرُ

58/422 تاريخ دمشق لابن عساكر