Hadith 952
Anas (May Allah be pleased with him) reported:
عن أنس رضي الله عنه قال: قال رسول الله صلى الله عليه وسلم : "ما من مسلم يموت له ثلاثة لم يبلغوا الحنث إلا ادخله الله الجنة بفضل رحمته إياهم" ((متفق عليه)).
The Messenger of Allah (ﷺ) said, "Any Muslim who loses three children before they reach the age of maturity, will be granted Jannah by Allah, the Exalted, out of His Mercy for them." [Al-Bukhari and Muslim].
In plain words
Any Muslim who loses three children before they reach maturity is promised Paradise by Allah, out of His mercy toward those little ones.
Reference : Riyad as-Salihin 952 In-book reference : Book 6, Hadith 59