Sunan Ibn Majah, Chapter: The Book of the Sunnah

We returned with the Messenger of Allah (saw) from his Hajj that he had performed, and we stopped at some point on the road. He commanded that prayer should be performed in congregation, then he took the hand of 'Ali and said: 'Am I not dearer to the believers than their own selves?' They said: 'Yes indeed.' He said: 'Am I not dearer to every believer than their own selves?' They said: 'Yes indeed.' He said: "This man is the friend of those whose master I am.' O Allah, take as friends those who take him as a friend, and take enemies those who take him as an enemy.'" (Da'if)