What is the ruling on filling gaps and spaces in congregational prayer, what is its evidence, and do the Hanafis dislike it?

The Hanafis, like other scholars, require the straightening of rows, standing shoulder to shoulder, and filling gaps in prayer. It is sunnah for the Imam to command this, based on the Prophet's (peace be upon him) saying: "Straighten your rows, for straightening the rows is part of the perfection of prayer," and "You must straighten your rows or Allah will cause discord in your faces."