كتاب القدر
46  
The Book of Destiny
(6)
Chapter: The Meaning Of "Every Child Is Born In A State Of Fitrah" And The Ruling On The Dead Children Of The Disbelievers And Of The Muslims.
(6)
بَاب مَعْنَى كُلِّ مَوْلُودٍ يُولَدُ عَلَى الْفِطْرَةِ وَحُكْمِ مَوْتِ أَطْفَالِ الْكُفَّارِ وَأَطْفَالِ الْمُسْلِمِينَ
Sahih Muslim 2662 b

'A'isha, the mother of the believers, reported that a child died and I said:

There is happiness for this child who is a bird from amongst the birds of Paradise. Thereupon Allah's Messenger (ﷺ) said: Don't you know that Allah created the Paradise and He created the Hell and He created the dwellers for this (Paradise) and the denizens for this (Hell)?
حَدَّثَنِي زُهَيْرُ بْنُ حَرْبٍ، حَدَّثَنَا جَرِيرٌ، عَنِ الْعَلاَءِ بْنِ الْمُسَيَّبِ، عَنْ فُضَيْلِ بْنِ عَمْرٍو، عَنْ عَائِشَةَ بِنْتِ طَلْحَةَ، عَنْ عَائِشَةَ أُمِّ الْمُؤْمِنِينَ، قَالَتْ تُوُفِّيَ صَبِيٌّ فَقُلْتُ طُوبَى لَهُ عُصْفُورٌ مِنْ عَصَافِيرِ الْجَنَّةِ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ أَوَلاَ تَدْرِينَ أَنَّ اللَّهَ خَلَقَ الْجَنَّةَ وَخَلَقَ النَّارَ فَخَلَقَ لِهَذِهِ أَهْلاً وَلِهَذِهِ أَهْلاً ‏"‏ ‏.‏
Reference : Sahih Muslim 2662b
In-book reference : Book 46, Hadith 46
USC-MSA web (English) reference : Book 33, Hadith 6435
  (deprecated numbering scheme)