Sayyiduna al-Harith bin Uqaysh (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: "Any two Muslims (husband and wife) whose four children die, Allah Almighty will admit them both (husband and wife) into Paradise by the grace of His mercy." The people said: "O Messenger of Allah! And if there are three?" The Prophet (peace and blessings be upon him) said: "And if three (have died, this reward will be attained too)." The people said: "And if there are two?" The Prophet (peace and blessings be upon him) said: "And if there are two (the same reward will be attained)."
Abdullah bin Ahmad, Imam al-Tabarani in al-Mu'jam al-Kabir, and Imam Abu Ya'la recorded it, and its narrators are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الجنائز / 3983