The Rites of Hajj (Kitab Al-Manasik Wa'l-Hajj)
Dawud :: Book 10 : Hadith 1948
Narrated Sarra' daughter of Nabhan:
She was mistress of a temple in pre-Islamic days. She said: The prophet (peace_be_upon_him) addressed us on the second day of sacrifice (yawm ar-ru'us) and said: Which is this day? We said: Allah and His Apostle are better aware. He said: Is this not the middle of the tashriq days?