Ibn 'Abbas says about the Aayah, "Remember Allaah during the well known days," that it refers to the first ten days of Dhul-Hijjah. [This is related by al-Bukhari]
Allaah swears an oath by them, and swearing an oath by something is indicative of its importance and great benefit. Allaah says (interpretation of the meaning): "By the dawn; by the 10 nights" [al-Fajr 89:1-2]. Ibn Abbaas, Ibn al-Zubayr, Mujaahid and others of the earlier and later generations said that this refers to the first ten days of Dhul-Hijjah. Ibn Katheer said: "This is the correct opinion." [Tafseer Ibn Katheer, 8/413]
