Sahih Muslim 2403 a
Abu Musa al-Ash'ari reported that while Allah's Messenger (ﷺ) 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 (ﷺ) 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 Prophet had said). Thereupon he said: O Allah, grant me steadfastness. Allah is one Whose help is to be sought.
حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى الْعَنَزِيُّ، حَدَّثَنَا ابْنُ أَبِي عَدِيٍّ، عَنْ عُثْمَانَ بْنِ غِيَاثٍ، عَنْ 
 أَبِي عُثْمَانَ النَّهْدِيِّ، عَنْ أَبِي مُوسَى الأَشْعَرِيِّ، قَالَ بَيْنَمَا رَسُولُ اللَّهِ صلى الله عليه وسلم
 فِي حَائِطٍ مِنْ حَائِطِ الْمَدِينَةِ وَهُوَ مُتَّكِئٌ يَرْكُزُ بِعُودٍ مَعَهُ بَيْنَ الْمَاءِ وَالطِّينِ إِذَا اسْتَفْتَحَ رَجُلٌ
 فَقَالَ ‏"‏ افْتَحْ وَبَشِّرْهُ بِالْجَنَّةِ ‏"‏ ‏.‏ قَالَ فَإِذَا أَبُو بَكْرٍ فَفَتَحْتُ لَهُ وَبَشَّرْتُهُ بِالْجَنَّةِ - قَالَ
 - ثُمَّ اسْتَفْتَحَ رَجُلٌ آخَرُ فَقَالَ ‏"‏ افْتَحْ وَبَشِّرْهُ بِالْجَنَّةِ ‏"‏ ‏.‏ قَالَ فَذَهَبْتُ فَإِذَا هُوَ عُمَرُ
 فَفَتَحْتُ لَهُ وَبَشَّرْتُهُ بِالْجَنَّةِ ثُمَّ اسْتَفْتَحَ رَجُلٌ آخَرُ - قَالَ - فَجَلَسَ النَّبِيُّ صلى الله عليه
 وسلم فَقَالَ ‏"‏ افْتَحْ وَبَشِّرْهُ بِالْجَنَّةِ عَلَى بَلْوَى تَكُونُ ‏"‏ ‏.‏ قَالَ فَذَهَبْتُ فَإِذَا هُوَ عُثْمَانُ
 بْنُ عَفَّانَ - قَالَ - فَفَتَحْتُ وَبَشَّرْتُهُ بِالْجَنَّةِ - قَالَ - وَقُلْتُ الَّذِي قَالَ فَقَالَ اللَّهُمَّ صَبْرًا
 أَوِ اللَّهُ الْمُسْتَعَانُ ‏.‏