Musnad Abu Ya'la al-Mawsili 42:174

Uqbah narrated to us, Yunus narrated to us, Ibn Ishaq narrated to us, from Ubayd Allah ibn al-Mughirah, from Sulayman ibn Amr, from Abu Sa’id al-Khudri, that the Messenger of Allah (ﷺ) said: "Paradise was presented to me, and I went to take a cluster from it to show it to you, but it was placed between me and it. A man said: 'O Messenger of Allah, is it like the size of a grape?' He said: 'Like the greatest bucket. May your mother be bereaved of you.'"