Musnad Ahmad 30:3491

Ishaq narrated to us, Awf informed us, from Muhammad ibn Sirin, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "There are no two Muslims who have three children die for them who have not reached the age of puberty, except that Allah will cause them and their parents to enter Paradise by the grace of His mercy." He said: "It will be said to them: 'Enter Paradise.' They will say: 'Until our parents come.'" He said this three times. They will say the same thing. He said: "Then it will be said to them: 'Enter Paradise, you and your parents.'"