Sahih Bukhari Volume 9, Book 92, Hadith Number 442.

Narrated By ‘Umar : The Prophet said to me, “Someone came to me tonight from my Lord while I was in the ‘Aqiq (valley), and said to me, “Offer prayer in this blessed valley and say: ‘Labbaik’ for the (performance of) ‘Umra and Hajj.”