Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1873
Iyas b. Salama b. Akwa' reported on the authority of his father, saying: We used to observe the Friday prayer with the Messenger of Allah (may peace be upon him), and when we returned we did not find the shadow of the walls in which we could take protection (from the heat of the sun).