The sin of him who does not fulfil his vow

Narrated Zahdam bin Mudarrab:

'Imran bin Hussain said, "The Prophet ﷺ said, 'The best of you (people) are my generation, and the second best will be those who will follow them, and then those who will follow the second generation." Imran added, "I do not remember whether he mentioned two or three (generations) after his generation. He added, 'Then will come some people who will make vows but will not fulfill them;
and they will be dishonest and will not be trustworthy, and they will give their witness without being asked to give their witness, and fatness will appear among them.' "

حَدَّثَنَا مُسَدَّدٌ، عَنْ يَحْيَى، عَنْ شُعْبَةَ، قَالَ حَدَّثَنِي أَبُو جَمْرَةَ، حَدَّثَنَا زَهْدَمُ بْنُ مُضَرِّبٍ، قَالَ سَمِعْتُ عِمْرَانَ بْنَ حُصَيْنٍ، يُحَدِّثُ عَنِ النَّبِيِّ ﷺ قَالَ " خَيْرُكُمْ قَرْنِي، ثُمَّ الَّذِينَ يَلُونَهُمْ، ثُمَّ الَّذِينَ يَلُونَهُمْ ـ قَالَ عِمْرَانُ لاَ أَدْرِي ذَكَرَ ثِنْتَيْنِ أَوْ ثَلاَثًا بَعْدَ قَرْنِهِ ـ ثُمَّ يَجِيءُ قَوْمٌ يَنْذُرُونَ وَلاَ يَفُونَ، وَيَخُونُونَ وَلاَ يُؤْتَمَنُونَ، وَيَشْهَدُونَ وَلاَ يُسْتَشْهَدُونَ، وَيَظْهَرُ فِيهِمُ السِّمَنُ ".