Sahih Muslim Book 4, Hadith Number 1872.

Chapter : Excellence of one who listens to the Khutba with perfect silence.

Iyas b. Salama b. al-Akwa’ reported on the authority of his father: We used to observe the Friday prayer with the Messenger of Allah (may peace be upon him) when the sun passed the meridian and we then returned and tried to find out afternoon shadow (of the walls for protecting themselves from the heat of the sun).