Hadith Qudsi 105

105) Narrated Jabir Allah's Messenger  said: No other days are better to Allah than the first ten days of Hajj Month. The narrator said: A man asked: 0 Allah's Messenger! Are these days better or the similar number of days of fighting in the cause of Allah? The Prophet  said: These days are better than the same number of days of fighting for the sake of Allah . And no other day is better to Allah than the day of 'Arafah when Allah  descends to the lowest heaven (world's sky) and boasts of the people on earth to the inhabitants of heaven (angels) and says: Look at My slaves who have corne with grown hair covered with dust to perform Hajj. They have come from all directions hoping for My mercy though they haven't seen My punishment. So there is no other day than the day of 'Arafah when the people are released abundantly from Fire.

(This Haditb is considered sound by others, and reported by Ibn Hibban).