al-Zuhri ابن شهاب الزهري‎, محمد بن مسلم · The Book On The Mosques And The Congregations

The Prophet scratched some spittle from the prayer direction of the mosque.

"The Messenger of Allah said: 'A man's prayer in congregation is twenty-some levels higher than his prayer in his house or in the marketplace.'"

"The Messenger of Allah said: 'The prayer of a man in congregation is higher than his prayer on his own by twenty-four or twenty-five levels."

They heard the Prophet say on his pulpit: "People should desist from failing to attend the congregations, otherwise Allah will seal their hearts, and they will be among the negligent."