From Sahih Bukhari (Hadith 936):
Narrated Jabir bin `Abdullah:While we were praying (Jumua Khutba & prayer) with the Prophet (ﷺ), 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
Reference: Bukhari 936