Musnad Ahmad 30:2847

Waki' narrated to us, Sufyan narrated to us, from Abu al-Zinad, from al-A'raj, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not call the grape 'al-karm' (the noble/generous), for indeed, 'al-karm' is the Muslim man."