Sunan an-Nasa'i 3182
It was narrated that Al-Ahnaf bin Qais said:
"We set out as pilgrims and came to Al-Madinah intending to perform Hajj. While we were in our camping place unloading our mounts, someone came to us and said: 'The people have gathered in the Masjid and there is panis.' So we set out and found the people gathered around a group in the middle of the Masjid, among whom were 'Ali, Zubayr, Talhah and Sa'd bin Abi Waqas. While we were like that, 'Uthman, may Allah be pleased with him, came, wearing a yellow cloak with which he had covered his head. He said: 'Is Talhah here? Is Az-Zubair here? Is Sa'd here?' They said: 'Yes.' He said: 'I adjure you be the One beside Whom there is none worthy of worship, din't the Messenger of Allah (ﷺ) say: Whoever buys the Mirbad [1] of Banu so-and so, Allah will forgive him, and I bought it for twenty or twenty-five thousand, then I came to the Messenger of Allah (ﷺ) and told him, and he said: Add it to our Masjid and the reward for it will be yours?' They said: 'By Allah, yes.' He said: 'I adjure you by the One beside Whom there is none worthy of worship, didn't the Messenger of Allah (ﷺ) say: Whoever buys the well of Rumah, Allah will forgive him, so I bought it for such and such and amount, then I came to the Messenger of Allah (ﷺ) and told him, and he said: Give it to provide water for the Muslims, and the reward for it will be yours?' They said: 'By Allah, yes.' He said: 'I adjure you by the One beside Whom there is none worthy of worship, didn't the Messenger of Allah (ﷺ) say: Whoever equips these (men)- meaning the army of  Al-'Usrah (Tabuk) - Allah will forgive him, so I equipped them until they were not lacking even a rope or a bridle?' They said: 'By Allah, yes.' He said: 'O Allah, bear witness, O Allah, bear witness, O Allah, bear witness.'"

[1] Mirbad: A place for drying dates.
أَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا عَبْدُ اللَّهِ بْنُ إِدْرِيسَ، قَالَ سَمِعْتُ حُصَيْنَ بْنَ عَبْدِ الرَّحْمَنِ، يُحَدِّثُ عَنْ عَمْرِو بْنِ جَاوَانَ، عَنِ الأَحْنَفِ بْنِ قَيْسٍ، قَالَ خَرَجْنَا حُجَّاجًا فَقَدِمْنَا الْمَدِينَةَ وَنَحْنُ نُرِيدُ الْحَجَّ فَبَيْنَا نَحْنُ فِي مَنَازِلِنَا نَضَعُ رِحَالَنَا إِذْ أَتَانَا آتٍ فَقَالَ إِنَّ النَّاسَ قَدِ اجْتَمَعُوا فِي الْمَسْجِدِ وَفَزِعُوا ‏.‏ فَانْطَلَقْنَا فَإِذَا النَّاسُ مُجْتَمِعُونَ عَلَى نَفَرٍ فِي وَسَطِ الْمَسْجِدِ وَفِيهِمْ عَلِيٌّ وَالزُّبَيْرُ وَطَلْحَةُ وَسَعْدُ بْنُ أَبِي وَقَّاصٍ فَإِنَّا لَكَذَلِكَ إِذْ جَاءَ عُثْمَانُ رضى الله عنه عَلَيْهِ مُلاَءَةٌ صَفْرَاءُ قَدْ قَنَّعَ بِهَا رَأْسَهُ فَقَالَ أَهَا هُنَا طَلْحَةُ أَهَا هُنَا الزُّبَيْرُ أَهَا هُنَا سَعْدٌ قَالُوا نَعَمْ ‏.‏ قَالَ فَإِنِّي أَنْشُدُكُمْ بِاللَّهِ الَّذِي لاَ إِلَهَ إِلاَّ هُوَ أَتَعْلَمُونَ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ مَنْ يَبْتَاعُ مِرْبَدَ بَنِي فُلاَنٍ غَفَرَ اللَّهُ لَهُ ‏"‏ ‏.‏ فَابْتَعْتُهُ بِعِشْرِينَ أَلْفًا أَوْ بِخَمْسَةٍ وَعِشْرِينَ أَلْفًا فَأَتَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم فَأَخْبَرْتُهُ فَقَالَ ‏"‏ اجْعَلْهُ فِي مَسْجِدِنَا وَأَجْرُهُ لَكَ ‏"‏ ‏.‏ قَالُوا اللَّهُمَّ نَعَمْ ‏.‏ قَالَ أَنْشُدُكُمْ بِاللَّهِ الَّذِي لاَ إِلَهَ إِلاَّ هُوَ أَتَعْلَمُونَ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ مَنِ ابْتَاعَ بِئْرَ رُومَةَ غَفَرَ اللَّهُ لَهُ فَابْتَعْتُهَا بِكَذَا وَكَذَا فَأَتَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم فَقُلْتُ قَدِ ابْتَعْتُهَا بِكَذَا وَكَذَا قَالَ ‏"‏ اجْعَلْهَا سِقَايَةً لِلْمُسْلِمِينَ وَأَجْرُهَا لَكَ ‏"‏ ‏.‏ قَالُوا اللَّهُمَّ نَعَمْ ‏.‏ قَالَ أَنْشُدُكُمْ بِاللَّهِ الَّذِي لاَ إِلَهَ إِلاَّ هُوَ أَتَعْلَمُونَ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم نَظَرَ فِي وُجُوهِ الْقَوْمِ فَقَالَ ‏"‏ مَنْ يُجَهِّزْ هَؤُلاَءِ غَفَرَ اللَّهُ لَهُ ‏"‏ ‏.‏ يَعْنِي جَيْشَ الْعُسْرَةِ فَجَهَّزْتُهُمْ حَتَّى لَمْ يَفْقِدُوا عِقَالاً وَلاَ خِطَامًا ‏.‏ فَقَالُوا اللَّهُمَّ نَعَمْ ‏.‏ قَالَ اللَّهُمَّ اشْهَدِ اللَّهُمَّ اشْهَدِ اللَّهُمَّ اشْهَدْ ‏.‏