Hadithcore
Sahih Muslim, 2930 b
sahih

Abdullah b. Umar reported that Allah's Messenger (ﷺ) went along with him in the company of some persons and there was Umar b. Khattab also amongst them till they saw Ibn Sayyad as a young boy just on the threshold of adolescence playing with children near the battlement of Bani Mu'awiya; the rest of the hadith is the same but with these concluding words:

" Had his mother left him (to murmur) his matter would have become clear."

حَدَّثَنَا الْحَسَنُ بْنُ عَلِيٍّ الْحُلْوَانِيُّ، وَعَبْدُ بْنُ حُمَيْدٍ، قَالاَ حَدَّثَنَا يَعْقُوبُ، - وَهُوَ ابْنُ إِبْرَاهِيمَ بْنِ سَعْدٍ - حَدَّثَنَا أَبِي، عَنْ صَالِحٍ، عَنِ ابْنِ شِهَابٍ، أَخْبَرَنِي سَالِمُ بْنُ عَبْدِ اللَّهِ، أَنَّالله عليه وسلم وَمَعَهُ رَهْطٌ مِنْ أَصْحَابِهِ فِيهِمْ عُمَرُ بْنُ الْخَطَّابِ حَتَّى وَجَدَ ابْنَ صَيَّادٍ غُلاَمًا قَدْ نَاهَزَ الْحُلُمَ يَلْعَبُ مَعَ الْغِلْمَانِ عِنْدَ أُطُمِ بَنِي مُعَاوِيَةَ ‏.‏ وَسَاقَ الْحَدِيثَ بِمِثْلِ حَدِيثِ يُونُسَ إِلَى مُنْتَهَى حَدِيثِ عُمَرَ بْنِ ثَابِتٍ وَفِي الْحَدِيثِ عَنْ يَعْقُوبَ قَالَ قَالَ أُبَىٌّ - يَعْنِي فِي قَوْلِهِ لَوْ تَرَكَتْهُ بَيَّنَ - قَالَ لَوْ تَرَكَتْهُ أُمُّهُ بَيَّنَ أَمْرَهُ ‏.‏

References2 variants
In-Book Reference
Book 54, Hadith 119
USC-MSA web (English) reference
Book 41, Hadith 7001 (deprecated numbering scheme)