Musannaf Ibn Abi Shayba 23:112

Ibn Fudayl narrated to us, from Layth, from ‘Amr ibn Murrah, from Mu‘awiyah ibn Suwayd, from al-Bara’, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "The firmest handhold of Islam is love for the sake of Allah and hatred for the sake of Allah."