Musannaf Ibn Abi Shayba 27:537

Waki’ narrated to us, from Sufyan, from Abu al-Juhhaf, from Abu Hazim, from Abu Hurayrah, who said: He said—meaning the Prophet, peace and blessings of Allah be upon him—: "O Allah, I love them both, so love them both," meaning Hasan and Husayn.