The Rites of Hajj (Kitab Al-Manasik Wa'l-Hajj)
Dawud :: Book 10 : Hadith 1935
Narrated Abdullah ibn Abbas:
The Apostle of Allah (peace_be_upon_him) sent ahead some boys from Banu AbdulMuttalib on donkeys on the night of al-Muzdalifah. He began to pat our thighs (out of love) and said: O young! boys do not throw pebbles at the jamrah till the sun rises.