Allah (SWT) takes an Oath by the Ten Nights of Dhul-Hijjah:
وَٱلۡفَجۡرِ - وَلَيَالٍ عَشۡرٍ۬
I swear by the dawn, [89:1] and by the Ten Nights, [89:2]
قَالَهُ عَلِيّ وَابْن عَبَّاس وَعِكْرِمَة وَمُجَاهِد وَالسُّدِّيّ وَعَنْ مَسْرُوق وَمُحَمَّد بْن كَعْب الْمُرَاد بِهِ فَجْر يَوْم النَّحْر خَاصَّة
Some commentators, like Mujahid and 'Ikramah, refer this to the dawn of 'the Day of Sacrifice' on the tenth of Dhul Hijjah. A narration from Sayyidna Ibn 'Abbas (RA) concurs with this view. [Maariful Qur'aan & Tafseer Ibn Katheer]
وَاللَّيَالِي الْعَشْر الْمُرَاد بِهَا عَشْر ذِي الْحِجَّة كَمَا قَالَهُ اِبْن عَبَّاس وَابْن الزُّبَيْر وَمُجَاهِد وَغَيْر وَاحِد مِنْ السَّلَف وَالْخَلَف
According Sayyidna Ibn 'Abbas , Qatadah, Mujahid, Suddi, Dahhak, Kalbi and other leading commentators, the 'ten nights' refers to the [first] ten nights of Dhul Hijjah. [Maariful Qur'aan & Tafseer Ibn Katheer]
