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كتاب الجنائز
23  
Funerals (Al-Janaa'iz)
(79)
Chapter: If a boy becomes a Muslim and then dies, should a funeral prayer be offered for him? Should Islam be explained to a boy?
(79)
باب إِذَا أَسْلَمَ الصَّبِيُّ فَمَاتَ هَلْ يُصَلَّى عَلَيْهِ وَهَلْ يُعْرَضُ عَلَى الصَّبِيِّ الإِسْلاَمُ
Sahih al-Bukhari 1357

Narrated Ibn `Abbas:

My mother and I were among the weak and oppressed. I from among the children, and my mother from among the women.

حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا سُفْيَانُ، قَالَ قَالَ عُبَيْدُ اللَّهِ سَمِعْتُ ابْنَ عَبَّاسٍ ـ رضى الله عنهما ـ يَقُولُ كُنْتُ أَنَا وَأُمِّي، مِنَ الْمُسْتَضْعَفِينَ أَنَا مِنَ الْوِلْدَانِ، وَأُمِّي، مِنَ النِّسَاءِ‏.‏
Reference : Sahih al-Bukhari 1357
In-book reference : Book 23, Hadith 110
USC-MSA web (English) reference : Vol. 2, Book 23, Hadith 439
  (deprecated numbering scheme)