It is narrated from Sayyidah Umm Sulaym bint Milhan (may Allah be pleased with her); she said: the Messenger of Allah (peace and blessings be upon him) said: "Any Muslim husband and wife who have three children die before reaching puberty, Allah will admit them into Paradise by the bounty of His mercy."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21768