Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: The "appointed days" [Surah al-Hajj: 28] are the ten days, and the "counted days" [Surah al-Baqarah: 203] are the days of Tashriq.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10145
Amr bin Dinar (may Allah have mercy on him) said: I saw Ibn Abbas (may Allah be pleased with them both) saying the takbir on the day of departure (from Mina) in Makkah and reciting: "And remember Allah during the counted days." [Surah al-Baqarah: 203]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10146
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