The Book Pertaining to the Merits of the Companions (Allah Be Pleased With Them) of the Holy Prophet (May Peace Be Upon Him) (Kitab Al-Fada'il Al-Sahabah)
Muslim :: Book 31 : Hadith 5909
Abu Musa al-Ash'ari reported that while Allah's Messenger (may peace be upon him) was in one of the gardens of Medina, reclining against a pillow and fixing a stick in a mud, that a person came asking for the gate to be opened, whereupon he said: Open it for him and give him glad tidings of Paradise and, lo, it was Abu Bakr. I opened (the gate) for him and gave him the glad tidings of Paradise. Then another person asked for the door to be opened, whereupon he said: Open it and give him the glad tidings of Piradise. He said: I went away and, lo, it was 'Umar. I opened it for him and gave him the glad tidings of Paradise. Then still another man asked for the door to be opened, and thereupon Allah's Apostle (may peace be upon him) said: Open it and give him the glad tidings of Paradise after a trial would afflict him. I went and, lo, it was 'Uthman b. 'Affan. 1 opened the door and gave him the glad tidings of Paradise and informed him (what the Holy Prophet had said). Thereupon he said: O Allah, grant me steadfastness. Allah is one Whose help is to be sought.