Abdullah Ibn ’Abbas (ra) related that the Prophet said, "Good deeds performed on other days are not superior to those performed on these (first ten days of Dhul Hijjah)."
The Companions (ra) inquired, "Not even Jihad?" He replied, "Not even Jihad, except for that person who goes out putting himself and his wealth in danger and does not return with anything." (Bukhari)
The Prophet said, “There are no days that are greater before Allah or in which good deeds are more beloved to Him than these ten days, so recite a great deal of tahleel, takbeer and tahmeed during them.” [Ahmad]