Musnad Abu Ya'la al-Mawsili 3:208

Abu Bakr narrated to us, Mus'ab ibn al-Miqdam narrated to us, Mandil narrated to us, from al-Hasan ibn al-Hakam, from Asma' bint 'Abis, from her father, from Ali, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Verily, the miscarried fetus will surely contend with its Lord if He enters its parents into the Fire, until it is said to it: 'O you miscarried fetus who contends with its Lord, return, for I have entered your parents into Paradise.' He said: Then it will drag them by its umbilical cord until it enters them into Paradise."