Is fasting the first nine days of Dhul-Hijjah from the Sunnah or not?

Fasting nine days of Dhul-Hijjah (excluding the Eid day) is a confirmed Sunnah, due to what was authentically reported from Hafsah (may Allah be pleased with her) that the Prophet (peace and blessings of Allah be upon him) never used to abandon them. The interpretation of Aisha's (may Allah be pleased with her) narration, that she never saw him fasting the ten days at all, is that this was due to an excuse such as illness, travel, or the like, or because his fasting might not have been apparent. The most emphasized of these days is the Day of Arafah for those not performing Hajj, then the Day of Tarwiyah, then the remaining days.