Musnad Abu Ya'la al-Mawsili 3:250

Ibrahim ibn Sa'id narrated to us, Husayn ibn Muhammad narrated to us, from 'Amr ibn Thabit, from his father, from Abu Fakhitah, from 'Ali, who said: The Messenger of Allah (ﷺ) said to Fatimah: "Indeed, I, you, this one—meaning myself—and these two, al-Hasan and al-Husayn, will be in one place on the Day of Resurrection."