Sahih al-Bukhari 861
Sahih al-Bukhari · Book 10: Call to Prayers (Adhaan) · The ablution for boys (youngsters). When they should perform Ghusl (take a bath) and Tuhur (purification). Their attendance at congregational prayers and their rows in the prayers.
Narrated Ibn `Abbas:
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ ، عَنْ مَالِكٍ ، عَنِ ابْنِ شِهَابٍ ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ بْنِ عُتْبَةَ ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ أَنَّهُ قَالَ أَقْبَلْتُ رَاكِبًا عَلَى حِمَارٍ أَتَانٍ وَأَنَا يَوْمَئِذٍ قَدْ نَاهَزْتُ الاِحْتِلاَمَ وَرَسُولُ اللَّهِ صلى الله عليه وسلم يُصَلِّي بِالنَّاسِ بِمِنًى إِلَى غَيْرِ جِدَارٍ، فَمَرَرْتُ بَيْنَ يَدَىْ بَعْضِ الصَّفِّ، فَنَزَلْتُ وَأَرْسَلْتُ الأَتَانَ تَرْتَعُ وَدَخَلْتُ فِي الصَّفِّ، فَلَمْ يُنْكِرْ ذَلِكَ عَلَىَّ أَحَدٌ.
Once I came riding a she-ass and I, then, had just attained the age of puberty. Allah's Messenger (ﷺ) was leading the people in prayer at Mina facing no wall. I passed in front of the row and let loose the sheass for grazing and joined the row and no one objected to my deed.