Musnad Ahmad 1017:34

Ibn Numayr narrated to us, from Sharik, Abu Rabi‘ah narrated to us, from Ibn Buraydah, from his father, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, Allah loves four of my companions; He informed me that He loves them, and He commanded me to love them." They said: "Who are they, O Messenger of Allah?" He said: "Indeed, ‘Ali is among them, and Abu Dharr al-Ghifari, and Salman al-Farisi, and al-Miqdad ibn al-Aswad al-Kindi."