Musnad Ahmad 30:3792

Muhammad ibn Abdullah narrated to us, Yahya ibn Ayyub narrated to us, from the descendants of Jarir, he said: I heard Abu Zur'ah mentioning, from Abu Hurairah, he said: A woman came to the Messenger of Allah, may Allah bless him and grant him peace, with a sick child of hers, for him to pray for his healing and well-being. She said: "O Messenger of Allah, three [of my children] have died." He said: "In Islam?" She said: "In Islam." He said: "There is no Muslim who sends ahead three [children] in Islam who have not reached the age of puberty, seeking their reward from Allah, except that he will be shielded by a barrier from the Fire."