Sunan An-Nasa'i - سنن النسائي
10. The Book of Leading the Prayer (Al-Imamah) - كتاب الإمامة
22) Chapter: Where the Imam should stand when the person praying with him is a boy
It was narrated that Ibn Abbas said:
"I stayed overnight with my maternal aunt Maimunah, and the Messenger of Allah (ﷺ) got up to pray at night. I stood on his left, so he did this to me: He took me by the head and made me stand on
his right."
22) باب مَوْقِفِ الإِمَامِ وَالْمَأْمُومُ صَبِيٌّ
أَخْبَرَنَا يَعْقُوبُ بْنُ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا ابْنُ عُلَيَّةَ، عَنْ أَيُّوبَ، عَنْ عَبْدِ اللَّهِ بْنِ سَعِيدِ بْنِ جُبَيْرٍ، عَنْ أَبِيهِ، عَنِ ابْنِ عَبَّاسٍ، قَالَ بِتُّ عِنْدَ خَالَتِي مَيْمُونَةَ فَقَامَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُصَلِّي مِنَ اللَّيْلِ فَقُمْتُ عَنْ شِمَالِهِ فَقَالَ بِي هَكَذَا فَأَخَذَ بِرَأْسِي فَأَقَامَنِي عَنْ يَمِينِهِ .