The Messenger of Allah ﷺ said, "Whoever has lost three children who had not reached the age of accountability, they will be a strong fortress for him against the Fire."Abu Darda said, "I have lost two."He replied, "And two as well."Then Ubayy bin Kaab, Abu Mundhir, the master of the reciters, said, "I have lost one."He replied, "And one as well, but that applies only at the first shock of grief."
حدثنا محمد بن يزيد قال أخبرنا العوام حدثنا أبو محمد مولى لعمر بن الخطاب
قال رسول الله ﷺ من قدم ثلاثة لم يبلغوا الحنث كانوا له حصنا حصينا من النار فقال أبو الدرداء قدمت اثنين قال واثنين فقال أبي بن كعب أبو المنذر سيد القراء قدمت واحدا قال وواحد ولكن ذاك في أول صدمة
Its chain of transmission is daif because of a break in it. We previously discussed it in detail at 3554, where we referred to this chain and the two chains after it. Something similar in meaning has already passed with a sahih chain at 3995. Something similar will also come from the hadith of Abu Hurairah at 7351.