Fasting During Dhul-Hijjah Equals a Year's Fasts; Its Nights Equal Laylat al-Qadr

❀ Question:
Is it true that fasting during the days of Dhul-Hijjah is equal to fasting for an entire year?
✿ Answer:
الحمد لله، والصلاة والسلام علىٰ رسول الله، أما بعد
① Ḥadīth of Abū Hurayrah رضي الله عنه
It is narrated from Abū Hurayrah رضي الله عنه that the Prophet ﷺ said:
"مَا مِنْ أَيَّامٍ أَحَبُّ إِلَى اللَّهِ أَنْ يُتَعَبَّدَ لَهُ فِيهَا مِنْ عَشْرِ ذِي الحِجَّةِ، يَعْدِلُ صِيَامُ كُلِّ يَوْمٍ مِنْهَا بِصِيَامِ سَنَةٍ، وَقِيَامُ كُلِّ لَيْلَةٍ مِنْهَا بِقِيَامِ لَيْلَةِ القَدْرِ"
“There are no days more beloved to Allah in which acts of worship are performed than the ten days of Dhul-Hijjah. The fast of each day is equivalent to fasting for an entire year, and the worship of each night is equivalent to the worship of Laylat al-Qadr.”

Note on Authenticity:
This narration is somewhat weak in terms of its chain of transmission.
Conclusion:
◈ The narration indicates immense virtues for fasting during the first ten days of Dhul-Hijjah and worshipping during their nights.
◈ While the narration is not very strong, the general encouragement to engage in worship during these days is well established in authentic narrations.
وَاللّٰهُ أَعْلَمُ بِالصَّوَاب