The Rites of Hajj (Kitab Al-Manasik Wa'l-Hajj)
Dawud :: Book 10 : Hadith 1964
Narrated Abdullah ibn Umar:
Nafi' reported on the authority of Ibn Umar. He (ibn Umar) used to come (to Mina) and threw pebbles three days after the day of sacrifice walking when arriving and returning (both ways). He reported that the Prophet (peace_be_upon_him) used to do so.