What is the virtue of the first ten days of Dhu al-Hijjah, and what is the proof for that from the Sunnah?

The first ten days of Dhul-Hijjah are among the best and greatest days in the sight of Allah Almighty. Good deeds performed during them are beloved. The Prophet, peace and blessings be upon him, clarified that the best days of the world are these ten, and that performing good deeds during them is superior to striving in the way of Allah, except for a man who goes forth risking his life and wealth and returns with nothing.