From Sahih Bukhari (Hadith 1249):
Narrated Abu Sa`id:The women requested the Prophet, "Please fix a day for us." So the Prophet (ﷺ) preached to them and said, "A woman whose three children died would be screened from the Hell Fire by them," Hearing that, a woman asked, "If two died?" The Prophet (ﷺ) replied, "Even two (would screen her from the (Hell) Fire. " And Abu Huraira added, "Those children should be below the age of puberty
Reference: Bukhari 1249