What are the permissible distances between worshippers in congregational prayer, and to what extent are the worshipper and the imam responsible for that?

There should be no space between worshipers in the same row, and the Sunnah is for each of them to press his shoulder against his neighbor's shoulder and his foot against his foot, in compliance with the Prophet's (peace be upon him) command: "Straighten your rows, for I see you from behind my back," and "Complete the rows, align shoulders, fill the gaps, and do not leave openings for Satan." The Prophet (peace be upon him) also emphasized the straightening of rows, warning against diverging from it, saying: "You must straighten your rows, or Allah will cause discord between your faces."