Abu Hurairah (May Allah be pleased with him)reported:
The Messenger of Allah ﷺ said, "Let the Imam stand in the middle (so that those praying behind him should be standing both on his right and his left) and close the gaps."

[Abu Dawud].

وعن أبي هريرة رضي الله عنه قال قال رسول الله ﷺ: "وسطوا الإمام، وسدوا الخلل" ((رواه أبو داود)).