Riyad as-Salihin 17:230

Abu Hurairah (May Allah be pleased with him) said:

The Messenger of Allah (ﷺ) 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."