Al-Qasim ibn Muhammad reported: Umar ibn al-Khattab had married a woman of the Ansar and she gave birth to ‘Asim ibn Umar, then he divorced her. Umar came to Quba’ and he found his son ‘Asim playing in the courtyard of the mosque. He took him by the arm and placed him in front of him on his mount. The grandmother of the boy noticed him and argued with him until they were brought before Abu Bakr al-Siddiq, may Allah be pleased with him. Umar said, “He is my son.” The mother said, “He is my son.” Abu Bakr said, “Leave him and her together.” Umar did not repeat what he had said.
Source: al-Muwaṭṭa’ 1498
عَنْ الْقَاسِم بْن مُحَمَّدٍ قَالَ كَانَتْ عِنْدَ عُمَرَ بْنِ الْخَطَّابِ امْرَأَةٌ مِنْ الْأَنْصَارِ فَوَلَدَتْ لَهُ عَاصِمَ بْنَ عُمَرَ ثُمَّ إِنَّهُ فَارَقَهَا فَجَاءَ عُمَرُ قُبَاءً فَوَجَدَ ابْنَهُ عَاصِمًا يَلْعَبُ بِفِنَاءِ الْمَسْجِدِ فَأَخَذَ بِعَضُدِهِ فَوَضَعَهُ بَيْنَ يَدَيْهِ عَلَى الدَّابَّةِ فَأَدْرَكَتْهُ جَدَّةُ الْغُلَامِ فَنَازَعَتْهُ إِيَّاهُ حَتَّى أَتَيَا أَبَا بَكْرٍ الصِّدِّيقَ رضي الله عنه فَقَالَ عُمَرُ ابْنِي وَقَالَتْ الْمَرْأَةُ ابْنِي فَقَالَ أَبُو بَكْرٍ خَلِّ بَيْنَهَا وَبَيْنَهُ قَالَ فَمَا رَاجَعَهُ عُمَرُ الْكَلَامَ
1498 موطأ مالك كتاب الوصية باب ما جاء في المؤنث من الرجال ومن أحق بالولد