Musnad Ahmad 5:567

'Abdullah narrated to us, 'Uthman ibn Abi Shaybah narrated to me, Muhammad ibn Fudayl narrated to us, from Muhammad ibn 'Uthman, from Zadhan, from 'Ali, who said: Khadijah asked the Prophet, peace and blessings of Allah be upon him, about two children of hers who died during the Jahiliyyah (pre-Islamic period). The Messenger of Allah, peace and blessings of Allah be upon him, said: "They are in the Fire." He said: When he saw the dislike on her face, he said: "If you had seen their place, you would have hated them." She said: "O Messenger of Allah, and my children from you?" He said: "In Paradise." He said: Then the Messenger of Allah, peace and blessings of Allah be upon him, said: "Indeed, the believers and their children are in Paradise, and the polytheists and their children are in the Fire." Then the Messenger of Allah, peace and blessings of Allah be upon him, recited: "And those who believed and whose descendants followed them in faith - We will join with them their descendants" [At-Tur: 21].