Sahih Muslim Book 4, Hadith Number 1881.

Chapter : Concerning the two sermons before the Friday prayer and sitting for a while between the two.

Ka’b b. ‘Ujra reported that he entered the mosque and saw Abd al-Rahman b. Umm Hakam delivering the sermon in a sitting posture. Upon this he said: Look at this wretched person; he delivers the sermon while sitting, whereas Allah said: “And when they see merchandise or sport, they break away to it and leave thee standing.”