Musnad Abu Ya'la al-Mawsili 148:8

Abdullah ibn Umar ibn Aban narrated to us, Abd al-Rahman ibn Muhammad narrated to us, from Muhammad ibn Ishaq, from Yazid ibn Abi Habib, from ibn Sinan Sa’d al-Kindi, from Anas ibn Malik, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "By the One in whose hand is my soul, Allah does not place His mercy except upon the merciful." They said: "O Messenger of Allah, all of us are merciful." He said: "It is not the mercy of one of you for his companion; [rather, it is that] he shows mercy to all people."