Musnad Ahmad 788:169

Ya'qub narrated to us, my father narrated to us, from Salih, who said: Abu al-Zinad narrated that Abu Salamah informed him, that 'Abd al-Rahman ibn Nafi' ibn 'Abd al-Harith al-Khuza'i informed him, that Abu Musa informed him: That the Messenger of Allah (may Allah bless him and grant him peace) was in a garden in Medina, at the edge of a well, dangling his legs. Then Abu Bakr (may Allah be pleased with him) knocked on the door. The Messenger of Allah (may Allah bless him and grant him peace) said: "Give him permission and give him glad tidings of Paradise." He did so, and Abu Bakr (may Allah be pleased with him) entered and dangled his legs. Then 'Umar (may Allah be pleased with him) knocked on the door. The Messenger of Allah (may Allah bless him and grant him peace) said to him: "Give him permission and give him glad tidings of Paradise." He did so. Then 'Uthman ibn 'Affan (may Allah be pleased with him) knocked on the door. The Messenger of Allah (may Allah bless him and grant him peace) said to him: "Give him permission and give him glad tidings of Paradise, and he will encounter a trial." He did so.