Riyad as-Salihin

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.]