Musnad Abu Ya'la al-Mawsili 115:126

Abu Khaythama narrated to us, Yahya narrated to us, from Husayn al-Mu'allim, from Qatada, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "By the One in Whose hand is my soul, a servant does not believe until he loves for his neighbor—or for his brother—what he loves for himself."