Musnad Abu Ya'la al-Mawsili 140:45

'Abd al-Ghaffar ibn 'Abd Allah narrated to us, Abu Shihab narrated to us, from al-A'mash, from Yazid al-Raqashi, from Anas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I will knock on the door of Paradise, and a door of gold with a ring of silver will be opened for me. Then the greatest light will meet me, so I will fall down prostrate. I will be inspired with praises for Allah that no one before me has been inspired with. It will be said to me: 'Raise your head, ask and you shall be given, speak and you shall be heard, and intercede and your intercession shall be accepted.' I will say: 'My Ummah.' It will be said to me: 'For you is whoever has in his heart the weight of a barleycorn of faith.' He said: Then I will prostrate a second time, and I will be inspired with the like of that, and it will be said to me the like of that. I will say: 'My Ummah.' It will be said to me: 'For you is whoever has in his heart the weight of a mustard seed of faith.' Then I will prostrate a third time, and it will be said to me the like of that. Then I will raise my head and say: 'My Ummah.' It will be said to me: 'For you is whoever said "There is no god but Allah" sincerely.'"