Sahih Al Bukhari Hadith Number 1081

Narrated Yahya bin ‘Is-haq: I heard Anas saying, “We traveled with the Prophet (peace be upon him) from Medina to Mecca and offered two rak`at (for every prayer) till we returned to Medina.” I said, “Did you stay for a while in Mecca?” He replied, “We stayed in Mecca for ten days.”

18  Shortening the Prayers (At-Taqseer)
Hadith number 1081
Volume no 2
Chapter: 1 (For what period of stay one should offer shortened prayers)