What is the ruling on fasting from the beginning of Dhu al-Hijjah until its ninth day?

It is recommended to fast the first nine days of Dhul-Hijjah, for righteous deeds performed therein are more beloved to Allah. It has been reported that the Prophet (peace be upon him) used to fast them. The statement of Aisha (may Allah be pleased with her), "I never saw the Messenger of Allah (peace be upon him) fasting in the Ten (days) at all," is interpreted to mean that he did not fast them due to an impediment, or that she did not see him fasting.