Musnad Abu Ya'la al-Mawsili 245:14

Masruq ibn al-Marzuban narrated to us, Ibn Abi Za'idah narrated to us, from Muhammad ibn 'Amr, from Abu Salamah, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever loves the Ansar, Allah loves him, and whoever hates the Ansar, Allah hates him."