Narrated Abu Musa Al-Ash'ari:

I went to Allah's Apostle along with a group of people from (the tribe of) Al-Ash'ari, asking for mounts. The Prophet ﷺ said, "By Allah, I will not give you anything to ride, and I have nothing to mount you on." We stayed there as long as Allah wished, and after that, some camels were brought to the Prophet and he ordered that we be given three camels. When we set out, some of us said to others, "Allah will not bless us, as we all went to Allah's Apostle asking him for mounts, and although he had sworn that he would not give us mounts, he did give us." So we returned to the Prophet;
and mentioned that to him. He said, "I have not provided you with mounts, but Allah has. By Allah, Allah willing, if I ever take an oath, and then see that another is better than the first, I make expiration for my (dissolved) oath, and do what is better and make expiration."

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا حَمَّادٌ، عَنْ غَيْلاَنَ بْنِ جَرِيرٍ، عَنْ أَبِي بُرْدَةَ بْنِ أَبِي مُوسَى، عَنْ أَبِي مُوسَى الأَشْعَرِيِّ، قَالَ أَتَيْتُ رَسُولَ اللَّهِ ﷺ فِي رَهْطٍ مِنَ الأَشْعَرِيِّينَ أَسْتَحْمِلُهُ فَقَالَ " وَاللَّهِ لاَ أَحْمِلُكُمْ، مَا عِنْدِي مَا أَحْمِلُكُمْ ". ثُمَّ لَبِثْنَا مَا شَاءَ اللَّهُ، فَأُتِيَ بِإِبِلٍ فَأَمَرَ لَنَا بِثَلاَثَةِ ذَوْدٍ، فَلَمَّا انْطَلَقْنَا قَالَ بَعْضُنَا لِبَعْضٍ لاَ يُبَارِكُ اللَّهُ لَنَا، أَتَيْنَا رَسُولَ اللَّهِ ﷺ نَسْتَحْمِلُهُ فَحَلَفَ أَنْ لاَ يَحْمِلَنَا فَحَمَلَنَا. فَقَالَ أَبُو مُوسَى فَأَتَيْنَا النَّبِيَّ ﷺ فَذَكَرْنَا ذَلِكَ لَهُ فَقَالَ " مَا أَنَا حَمَلْتُكُمْ بَلِ اللَّهُ حَمَلَكُمْ، إِنِّي وَاللَّهِ إِنْ شَاءَ اللَّهُ لاَ أَحْلِفُ عَلَى يَمِينٍ فَأَرَى غَيْرَهَا خَيْرًا مِنْهَا، إِلاَّ كَفَّرْتُ عَنْ يَمِينِي، وَأَتَيْتُ الَّذِي هُوَ خَيْرٌ وَكَفَّرْتُ ".