Musnad Ahmad 435:92

Yazid ibn Harun narrated to us, Yahya ibn Sa'id informed us, that Sa'd ibn Ibrahim informed him, from al-Hakam ibn Mina, that Yazid ibn Jariyah informed him that he was sitting among a group of the Ansar. Mu'awiyah came out to them and asked them about their conversation. They said: "We were in a conversation regarding the affairs of the Ansar." Mu'awiyah said: "Shall I not add to your conversation a hadith I heard from the Messenger of Allah, peace and blessings of Allah be upon him?" They said: "Yes, O Commander of the Faithful." He said: "I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: 'Whoever loves the Ansar, Allah the Almighty loves him, and whoever hates the Ansar, Allah the Almighty hates him.'"