Mujahid (may Allah have mercy on him) said: "The appointed days" [Surah al-Hajj: 28] means the ten days, and "the numbered days" [Surah al-Baqarah: 203] means the days of Tashriq (that is, the 11th, 12th and 13th of Dhu al-Hijjah).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10147