Musnad Ahmad 32:572

Hashim ibn al-Qasim narrated to us, al-Mubarak narrated to us, Thabit al-Bunani narrated to us, from Anas ibn Malik, that a man said to the Prophet, peace and blessings of Allah be upon him: "I love such-and-such person." The Prophet, peace and blessings of Allah be upon him, said: "Have you informed him?" He said: "No." He said: "Inform him." He said: So he met him afterwards and said: "By Allah, I truly love you for the sake of Allah." He said to him: "May the One for whom you loved me love you."