Musnad Abu Ya'la al-Mawsili 117:145

Ali ibn al-Ja'd narrated to us, Mubarak ibn Fudalah narrated to us, from Thabit al-Bunani, from Anas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "No two men have ever loved one another for the sake of Allah, except that the better of the two was the one who was most intense in his love for his companion."