Riyad as-Salihin 6:60

Abu Hurairah (May Allah be pleased with him) reported:

The Messenger of Allah (ﷺ) said, "A Muslim whose three children die (in infancy) will not be touched by the Fire (of Hell) except for the fulfillment of Allah's Oath." [Al-Bukhari and Muslim] . [Allah's Oath here refers to His Ayah: "There is not one of you but will cross over it (Hell)." (19:71) And the crossing will be across the 'Bridge' set over the Hell.]