Musnad Ahmad 30:603

'Abd al-Razzaq narrated to us, he said: Ma'mar said: Al-Zuhri informed me, from Ibn al-Musayyib, from Abu Hurayrah, that the Prophet, peace and blessings of Allah be upon him, said: "Whoever has three [children] die who have not reached the age of puberty, the Fire shall not touch him except for the fulfillment of the oath," meaning the arrival [at the Fire].