It is narrated from Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Love your friend moderately, for perhaps one day he may become your enemy; and dislike your enemy moderately, for perhaps one day he may become your friend."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13769