Anas ibn Malik · The Book On The Mosques And The Congregations

"The Messenger of Allah said: 'When anyone of you enters the mosque, let him send peace upon the prophet, then let him say: "Allahummaftah li abwaba rahmatika (O Allah, open to me the gates of Your mercy)." And when he leaves, let him say: "Allahumma inni as'aluka min fadlika. (O Allah, I ask of you from Your bounty)."

"The Messenger of Allah said: 'I was thinking of commanding that the call to prayer be given, then I would tell a man to lead the people in prayer, then I would go out with some other men carrying bundles of wood, and go to people who do not attend the prayer, and burn their houses down around them.'"