The Rites of Hajj (Kitab Al-Manasik Wa'l-Hajj)
Dawud :: Book 10 : Hadith 1933
Narrated Umar ibn al-Khattab:
The Arabs in the pre-Islamic period did not return from al-Muzdalifah till they saw sunlight at the mountain Thabir. The Prophet (peace_be_upon_him) opposed them and returned before the sunrise.