Fasting the (first) ten days (of Dhul-Hijjah)
حَدَّثَنَا عُمَرُ بْنُ شَبَّةَ بْنِ عَبِيدَةَ، حَدَّثَنَا مَسْعُودُ بْنُ وَاصِلٍ، عَنِ النَّهَّاسِ بْنِ قَهْمٍ، عَنْ قَتَادَةَ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، عَنْ أَبِي هُرَيْرَةَ، قَالَ: قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " مَا مِنْ أَيَّامِ الدُّنْيَا أَيَّامٌ، أَحَبُّ إِلَى اللَّهِ سُبْحَانَهُ أَنْ يُتَعَبَّدَ لَهُ فِيهَا، مِنْ أَيَّامِ الْعَشْرِ. وَإِنَّ صِيَامَ يَوْمٍ فِيهَا لَيَعْدِلُ صِيَامَ سَنَةٍ، وَلَيْلَةٍ فِيهَا بِلَيْلَةِ الْقَدْرِ " .
It was narrated from Abu Hurairah that the Messenger of Allah (ﷺ) said: “There are no days in this world during which worship is more beloved to Allah, Glorious is He, than the (first) ten days (of Dhul- Hijjah). Fasting one of these days is equivalent to fasting for one year, and one night of them is equal to Lailatul-Qadr.”