Musannaf Ibn Abi Shayba 27:327

Yazid ibn Harun narrated to us, from Ibn Ishaq, from al-Zuhri, from Humayd ibn Abd al-Rahman, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "For every people of a deed, there is a gate from the gates of Paradise through which they are called by that deed. So for the people of fasting, there is a gate called al-Rayyan." Abu Bakr said: "O Messenger of Allah, is there anyone who will be called from all of those gates?" He said: "Yes, and I hope that you will be one of them, O Abu Bakr."