Musnad Ahmad 1060:33

Abu Mu'awiyah narrated to us, Hajjaj narrated to us, from al-Zuhri, from Hakim ibn Bashir, from Abu Ayyub al-Ansari, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, the best of charity is charity given to a relative who harbors enmity."