Abu Hurairah (May Allah be pleased with him) said: The Messenger of Allah (PBUH) said, "None of you should use the word Al-Karm for grapes, for Al-Karm is a Muslim (worthy of respect)."[Al-Bukhari and Muslim]
Another narration is: "Verily, Al-Karm is the heart of a true believer."
Another narration is: "People have named grapes as Al-Karm; verily, only the heart of a believer is Al-Karm."
We learn from this Hadith that all the derivatives from the word Al-Karm can be used legitimately for Muslims only because Muslim is Karim. It is, therefore, wrong to call grapes as Karm.