The Rites of Hajj (Kitab Al-Manasik Wa'l-Hajj)
Dawud :: Book 10 : Hadith 1887
Narrated Abdullah ibn as-Sa'ib:
I heard the Apostle of Allah (peace_be_upon_him) say between the two corners: O Allah, bring us a blessing in this world and a blessing in the next and guard us from punishment of Hell.