Musnad Abu Ya'la al-Mawsili 159:143

Ishaq ibn Abi Isra'il narrated to us, Sufyan ibn 'Uyaynah narrated to us, from 'Ubayd Allah ibn Abi Yazid, from Nafi' ibn Jubayr ibn Mut'im, from Abu Hurayrah, who said: The Prophet, may Allah bless him and grant him peace, went out until he came to the house of Fatimah. She went out with him, and he said, "Is the little one there?" He said: So he was delayed. I thought that she was putting a necklace on him or washing him. He said: Then he—meaning al-Hasan—came running, and the Messenger of Allah, may Allah bless him and grant him peace, embraced him and said, "O Allah, I love him, so love him, and love whoever loves him."