Sahih Bukhari, Chapter: Friday Prayer

While we were praying (Jumua Khutba & prayer) with the Prophet (p.b.u.h), some camels loaded with food, arrived (from Sham.~ The people diverted their attention towards the camels (and left the mosque), and only twelve persons remained with the Prophet. So this verse was revealed: "But when they see Some bargain or some amusement, They disperse headlong to it, And leave you standing." (62.11)